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What is JavaScript ?

JavaScript is:

JavaScript is a lightweight, interpreted programming language
Designed for creating network-centric applications
Complementary to and integrated with Java
Complementary to and integrated with HTML
Open and cross-platform

JavaScript Syntax:

A JavaScript consists of JavaScript statements that are placed within the <script>... </script> HTML tags in a web page.

You can place the <script> tag containing your JavaScript anywhere within you web page but it is preferred way to keep it within the <head> tags.

The <script> tag alert the browser program to begin interpreting all the text between these tags as a script. So simple syntax of your JavaScript will be as follows

JavaScript code

</script>

The script tag takes two important attributes:

language: This attribute specifies what scripting language you are using. Typically, its value will be javascript. Although recent versions of HTML (and XHTML, its successor) have phased out the use of this attribute.
type: This attribute is what is now recommended to indicate the scripting language in use and its value should be set to "text/javascript".

So your JavaScript segment will look like:

JavaScript code

</script>

Your First JavaScript Script:

Let us write our class example to print out "Hello World".

<html>

<body>

<!--

document.write("Hello World!")

//-->

</script>

</body>

</html>

Above code will display following result:

Hello World!

Whitespace and Line Breaks:

JavaScript ignores spaces, tabs, and newlines that appear in JavaScript programs.

Because you can use spaces, tabs, and newlines freely in your program so you are free to format and indent your programs in a neat and consistent way that makes the code easy to read and understand.

Semicolons are Optional:

Simple statements in JavaScript are generally followed by a semicolon character, just as they are in C, C++, and Java. JavaScript, however, allows you to omit this semicolon if your statements are each placed on a separate line. For example, the following code could be written without semicolons

<!--

var1 = 10

var2 = 20

//-->

</script>

But when formatted in a single line as follows, the semicolons are required:

<!--

var1 = 10; var2 = 20;

//-->

</script>

Note: It is a good programming practice to use semicolons.

Case Sensitivity:

JavaScript is a case-sensitive language. This means that language keywords, variables, function names, and any other identifiers must always be typed with a consistent capitalization of letters.

So identifiers Time, TIme and TIME will have different meanings in JavaScript.

NOTE: Care should be taken while writing your variable and function names in JavaScript.

Comments in JavaScript:

JavaScript supports both C-style and C++-style comments, Thus:

Any text between a // and the end of a line is treated as a comment and is ignored by JavaScript.
Any text between the characters /* and */ is treated as a comment. This may span multiple lines.
JavaScript also recognizes the HTML comment opening sequence <!--. JavaScript treats this as a single-line comment, just as it does the // comment.
The HTML comment closing sequence --> is not recognized by JavaScript so it should be written as //-->.

JavaScript Placement in HTML File:

There is a flexibility given to include JavaScript code anywhere in an HTML document. But there are following most preferred ways to include JavaScript in your HTML file.

Script in <head>...</head> section.
Script in <body>...</body> section.
Script in <body>...</body> and <head>...</head> sections.
Script in and external file and then include in <head>...</head> section.

JavaScript DataTypes:

JavaScript allows you to work with three primitive data types:

Numbers eg. 123, 120.50 etc.
Strings of text e.g. "This text string" etc.
Boolean e.g. true or false.

JavaScript also defines two trivial data types, null and undefined, each of which defines only a single value.

JavaScript Variables:

Like many other programming languages, JavaScript has variables. Variables can be thought of as named containers. You can place data into these containers and then refer to the data simply by naming the container.

Before you use a variable in a JavaScript program, you must declare it. Variables are declared with the var keyword as follows:

<!--

var money;

var name;

//-->

</script>

JavaScript Variable Scope:

The scope of a variable is the region of your program in which it is defined. JavaScript variable will have only two scopes.

Global Variables: A global variable has global scope which means it is defined everywhere in your JavaScript code.
Local Variables: A local variable will be visible only within a function where it is defined. Function parameters are always local to that function.

JavaScript Variable Names:

While naming your variables in JavaScript keep following rules in mind.

You should not use any of the JavaScript reserved keyword as variable name. These keywords are mentioned in the next section. For example, break or boolean variable names are not valid.
JavaScript variable names should not start with a numeral (0-9). They must begin with a letter or the underscore character. For example, 123test is an invalid variable name but_123test is a valid one.
JavaScript variable names are case sensitive. For example, Name and name are two different variables.

JavaScript Reserved Words:

The following are reserved words in JavaScript. They cannot be used as JavaScript variables, functions, methods, loop labels, or any object names.

abstract
boolean
break
byte
case
catch
char
class
const
continue
debugger
default
delete
do
double

else
enum
export
extends
false
final
finally
float
for
function
goto
if
implements
import
in

instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
super

switch
synchronized
this
throw
throws
transient
true
try
typeof
var
void
volatile
while
with

What is an operator?

Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. JavaScript language supports following type of operators.

Arithmetic Operators
Comparision Operators
Logical (or Relational) Operators
Assignment Operators
Conditional (or ternary) Operators

The Arithmatic Operators:

There are following arithmatic operators supported by JavaScript language:

Assume variable A holds 10 and variable B holds 20 then:

Operator	Description	Example
+	Adds two operands	A + B will give 30
-	Subtracts second operand from the first	A - B will give -10
*	Multiply both operands	A * B will give 200
/	Divide numerator by denumerator	B / A will give 2
%	Modulus Operator and remainder of after an integer division	B % A will give 0
++	Increment operator, increases integer value by one	A++ will give 11
--	Decrement operator, decreases integer value by one	A-- will give 9

The Comparison Operators:

There are following comparison operators supported by JavaScript language

Assume variable A holds 10 and variable B holds 20 then:

Operator	Description	Example
==	Checks if the value of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

The Logical Operators:

There are following logical operators supported by JavaScript language

Assume variable A holds 10 and variable B holds 20 then:

Operator	Description	Example
&&	Called Logical AND operator. If both the operands are non zero then then condition becomes true.	(A && B) is true.
\|\|	Called Logical OR Operator. If any of the two operands are non zero then then condition becomes true.	(A \|\| B) is true.
!	Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.	!(A && B) is false.

The Bitwise Operators:

There are following bitwise operators supported by JavaScript language

Assume variable A holds 2 and variable B holds 3 then:

Operator	Description	Example
&	Called Bitwise AND operator. It performs a Boolean AND operation on each bit of its integer arguments.	(A & B) is 2 .
\|	Called Bitwise OR Operator. It performs a Boolean OR operation on each bit of its integer arguments.	(A \| B) is 3.
^	Called Bitwise XOR Operator. It performs a Boolean exclusive OR operation on each bit of its integer arguments. Exclusive OR means that either operand one is true or operand two is true, but not both.	(A ^ B) is 1.
~	Called Bitwise NOT Operator. It is a is a unary operator and operates by reversing all bits in the operand.	(~B) is -4 .
<<	Called Bitwise Shift Left Operator. It moves all bits in its first operand to the left by the number of places specified in the second operand. New bits are filled with zeros. Shifting a value left by one position is equivalent to multiplying by 2, shifting two positions is equivalent to multiplying by 4, etc.	(A << 1) is 4.
>>	Called Bitwise Shift Right with Sign Operator. It moves all bits in its first operand to the right by the number of places specified in the second operand. The bits filled in on the left depend on the sign bit of the original operand, in order to preserve the sign of the result. If the first operand is positive, the result has zeros placed in the high bits; if the first operand is negative, the result has ones placed in the high bits. Shifting a value right one place is equivalent to dividing by 2 (discarding the remainder), shifting right two places is equivalent to integer division by 4, and so on.	(A >> 1) is 1.
>>>	Called Bitwise Shift Right with Zero Operator. This operator is just like the >> operator, except that the bits shifted in on the left are always zero,	(A >>> 1) is 1.

The Assignment Operators:

There are following assignment operators supported by JavaScript language:

Operator	Description	Example
=	Simple assignment operator, Assigns values from right side operands to left side operand	C = A + B will assigne value of A + B into C
+=	Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand	C = A is equivalent to C = C A
/=	Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand	C %= A is equivalent to C = C % A

Miscellaneous Operator

The Conditional Operator (? :)

There is an oprator called conditional operator. This first evaluates an expression for a true or false value and then execute one of the two given statements depending upon the result of the evaluation. The conditioanl operator has this syntax:

Operator	Description	Example
? :	Conditional Expression	If Condition is true ? Then value X : Otherwise value Y

The typeof Operator

The typeof is a unary operator that is placed before its single operand, which can be of any type. Its value is a string indicating the data type of the operand.

The typeof operator evaluates to "number", "string", or "boolean" if its operand is a number, string, or boolean value and returns true or false based on the evaluation.

if statement:

The if statement is the fundamental control statement that allows JavaScript to make decisions and execute statements conditionally.

Syntax:

if (expression){

Statement(s) to be executed if expression is true

}

if...else statement:

The if...else statement is the next form of control statement that allows JavaScript to execute statements in more controlled way.

Syntax:

if (expression){

Statement(s) to be executed if expression is true

}else{

Statement(s) to be executed if expression is false

}

if...else if... statement:

The if...else if... statement is the one level advance form of control statement that allows JavaScript to make correct decision out of several conditions.

Syntax:

if (expression 1){

Statement(s) to be executed if expression 1 is true

}else if (expression 2){

Statement(s) to be executed if expression 2 is true

}else if (expression 3){

Statement(s) to be executed if expression 3 is true

}else{

Statement(s) to be executed if no expression is true

}

switch statement:

The basic syntax of the switch statement is to give an expression to evaluate and several different statements to execute based on the value of the expression. The interpreter checks each case against the value of the expression until a match is found. If nothing matches, adefault condition will be used.

switch (expression)

{

case condition 1: statement(s)

break;

case condition 2: statement(s)

break;

...

case condition n: statement(s)

break;

default: statement(s)

}

The while Loop

The most basic loop in JavaScript is the while loop which would be discussed in this tutorial.

Syntax:

while (expression){

Statement(s) to be executed if expression is true

}

The do...while Loop:

The do...while loop is similar to the while loop except that the condition check happens at the end of the loop. This means that the loop will always be executed at least once, even if the condition is false.

Syntax:

do{

Statement(s) to be executed;

} while (expression);

The for Loop

The for loop is the most compact form of looping and includes the following three important parts:

The loop initialization where we initialize our counter to a starting value. The initialization statement is executed before the loop begins.
The test statement which will test if the given condition is true or not. If condition is true then code given inside the loop will be executed otherwise loop will come out.
The iteration statement where you can increase or decrease your counter.

You can put all the three parts in a single line separated by a semicolon.

Syntax:

for (initialization; test condition; iteration statement){

Statement(s) to be executed if test condition is true

}

The for...in Loop

for (variablename in object){

statement or block to execute

}

In each iteration one property from object is assigned to variablename and this loop continues till all the properties of the object are exhausted.

The break Statement:

The break statement, which was briefly introduced with the switch statement, is used to exit a loop early, breaking out of the enclosing curly braces.

The continue Statement:

The continue statement tells the interpreter to immediately start the next iteration of the loop and skip remaining code block.

When a continue statement is encountered, program flow will move to the loop check expression immediately and if condition remain true then it start next iteration otherwise control comes out of the loop.

Functions:

A function is a group of reusable code which can be called anywhere in your programme. This eliminates the need of writing same code again and again. This will help programmers to write modular code. You can divide your big programme in a number of small and manageable functions.

Like any other advance programming language, JavaScript also supports all the features necessary to write modular code using functions.

You must have seen functions like alert() and write() in previous chapters. We are using these function again and again but they have been written in core JavaScript only once.

JavaScript allows us to write our own functions as well. This section will explain you how to write your own functions in JavaScript.

Function Definition:

Before we use a function we need to define that function. The most common way to define a function in JavaScript is by using the function keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block surrounded by curly braces. The basic syntax is shown here:

<!--

function functionname(parameter-list)

{

statements

}

//-->

</script>

Example:

A simple function that takes no parameters called sayHello is defined here:

<!--

function sayHello()

{

alert("Hello there");

}

//-->

</script>

Calling a Function:

To invoke a function somewhere later in the script, you would simple need to write the name of that function as follows:

<!--

sayHello();

//-->

</script>

Function Parameters:

Till now we have seen function without a parameters. But there is a facility to pass different parameters while calling a function. These passed parameters can be captured inside the function and any manipulation can be done over those parameters.

A function can take multiple parameters separated by comma.

Example:

Let us do a bit modification in our sayHello function. This time it will take two parameters:

<!--

function sayHello(name, age)

{

alert( name + " is " + age + " years old.");

}

//-->

</script>

Note: We are using + operator to concatenate string and number all together. JavaScript does not mind in adding numbers into strings.

Now we can call this function as follows:

<!--

sayHello('Zara', 7 );

//-->

</script>

The return Statement:

A JavaScript function can have an optional return statement. This is required if you want to return a value from a function. This statement should be the last statement in a function.

For example you can pass two numbers in a function and then you can expect from the function to return their multiplication in your calling program.

Example:

This function takes two parameters and concatenates them and return resultant in the calling program:

<!--

function concatenate(first, last)

{

var full;

full = first + last;

return full;

}

//-->

</script>

Now we can call this function as follows:

<!--

var result;

result = concatenate('Zara', 'Ali');

alert(result );

//-->

</script>

Exceptions

Exceptions can be handled with the common try/catch/finally block structure.

<!--

try {

statementsToTry

} catch ( e ) {

catchStatements

} finally {

finallyStatements

}

//-->

</script>

The try block must be followed by either exactly one catch block or one finally block (or one of both). When an exception occurs in the catch block, the exception is placed in e and the catch block is executed. The finally block executes unconditionally after try/catch.

Alert Dialog Box:

An alert dialog box is mostly used to give a warning message to the users. Like if one input field requires to enter some text but user does not enter that field then as a part of validation you can use alert box to give warning message as follows:

<head>

<!--

alert("Warning Message");

//-->

</script>

</head>

Confirmation Dialog Box:

A confirmation dialog box is mostly used to take user's consent on any option. It displays a dialog box with two buttons: OK and Cancel.

You can use confirmation dialog box as follows:

<head>

<!--

var retVal = confirm("Do you want to continue ?");

if( retVal == true ){

alert("User wants to continue!");

return true;

}else{

alert("User does not want to continue!");

return false;

}

//-->

</script>

</head>

Prompt Dialog Box:

You can use prompt dialog box as follows:

<head>

<!--

var retVal = prompt("Enter your name : ", "your name here");

alert("You have entered : " + retVal );

//-->

</script>

</head>

What is page redirection ?

When you click a URL to reach to a page X but internally you are directed to another page Y that simply happens because of page re-direction. This concept is different from JavaScript Page Refresh.

There could be various reasons why you would like to redirect from original page. I'm listing down few of the reasons:

You did not like the name of your domain and you are moving to a new one. Same time you want to direct your all visitors to new site. In such case you can maintain your old domain but put a single page with a page re-direction so that your all old domain visitors can come to your new domain.
You have build-up various pages based on browser versions or their names or may be based on different countries, then instead of using your server side page redirection you can use client side page redirection to land your users on appropriate page.
The Search Engines may have already indexed your pages. But while moving to another domain then you would not like to lose your visitors coming through search engines. So you can use client side page redirection. But keep in mind this should not be done to make search engine a fool otherwise this could get your web site banned.

How Page Re-direction works ?

Example 1:

This is very simple to do a page redirect using JavaScript at client side. To redirect your site visitors to a new page, you just need to add a line in your head section as follows:

<head>

<!--

window.location="http://www.newlocation.com";

//-->

</script>

</head>

Example 2:

You can show an appropriate message to your site visitors before redirecting them to a new page. This would need a bit time delay to load a new page. Following is the simple example to implement the same:

<head>

<!--

function Redirect()

{

window.location="http://www.newlocation.com";

}

document.write("You will be redirected to main page in 10 sec.");

setTimeout('Redirect()', 10000);

//-->

</script>

</head>

Here setTimeout() is a built-in JavaScript function which can be used to execute another function after a given time interval.

Example 3:

Following is the example to redirect site visitors on different pages based on their browsers :

<head>

<!--

var browsername=navigator.appName;

if( browsername == "Netscape" )

{

window.location="http://www.location.com/ns.htm";

}

else if ( browsername =="Microsoft Internet Explorer")

{

window.location="http://www.location.com/ie.htm";

}

else

{

window.location="http://www.location.com/other.htm";

}

//-->

</script>

</head>

The void is an important keyword in JavaScript which can be used as a unary operator that appears before its single operand, which may be of any type.

This operator specifies an expression to be evaluated without returning a value. Its syntax could be one of the following:

<head>

<!--

void func()

javascript:void func()

or:

void(func())

javascript:void(func())

//-->

</script>

</head>

Example 1:

The most common use for this operator is in a client-side javascript: URL, where it allows you to evaluate an expression for its side effects without the browser displaying the value of the evaluated expression.

Here the expression alert('Warning!!!') is evaluated but it is not loaded back into the current document:

<head>

<!--

//-->

</script>

</head>

<body>

<a href="javascript:void(alert('Warning!!!'))">Click me!</a>

</body>

Example 2:

Another example the following link does nothing because the expression "0" has no effect in JavaScript. Here the expression "0" is evaluated but it is not loaded back into the current document:

<head>

<!--

//-->

</script>

</head>

<body>

<a href="javascript:void(0))">Click me!</a>

</body>

Example 3:

Another use for void is to purposely generate the undefined value as follows:

<head>

<!--

function getValue(){

var a,b,c;

a = void ( b = 5, c = 7 );

document.write('a = ' + a + ' b = ' + b +' c = ' + c );

}

//-->

</script>

</head>

The Page Printing:

Many times you would like to give a button at your webpage to print out the content of that web page via an actual printer.

JavaScript helps you to implement this functionality using print function of window object.

The JavaScript print function window.print() will print the current web page when executed. You can call this function directly using onclick event as follows:

<head>

<!--

//-->

</script>

</head>

<body>

<form>

</form>

</body>

This will produce following button which let you print this page.

This serves your purpose to get page printed out, but this is not a recommended way of giving printing facility. A printer friendly page is really just a page with text, no images, graphics, or advertising.

You can do one of the followings to make a page printer friendly:

Make a copy of the page and leave out unwanted text and graphics, then link to that printer friendly page from the original. Check Example.
If you do not want to keep extra copy of a page then you can mark your printable text using proper comments like .....  and then you can use PERL or any other script in background to purge printable text and display for final printing. Our site is using same method to give print facility to our site visitors. Check Example.

How to print a page:

If someone is providing none of the above facilities then you can use browser's standard toolbar to get web pages printed out. Follow the link as follows:

File --> Print --> Click OK button.

Number Methods

The Number object contains only the default methods that are part of every object's definition.

Method	Description
constructor()	Returns the function that created this object's instance. By default this is the Number object.
toExponential()	Forces a number to display in exponential notation, even if the number is in the range in which JavaScript normally uses standard notation.
toFixed()	Formats a number with a specific number of digits to the right of the decimal.
toLocaleString()	Returns a string value version of the current number in a format that may vary according to a browser's locale settings.
toPrecision()	Defines how many total digits (including digits to the left and right of the decimal) to display of a number.
toString()	Returns the string representation of the number's value.
valueOf()	Returns the number's value.

Boolean Methods

Here is a list of each method and its description.

Method	Description
toSource()	Returns a string containing the source of the Boolean object; you can use this string to create an equivalent object.
toString()	Returns a string of either "true" or "false" depending upon the value of the object.
valueOf()	Returns the primitive value of the Boolean object.

String Methods

Here is a list of each method and its description.

Method	Description
charAt()	Returns the character at the specified index.
charCodeAt()	Returns a number indicating the Unicode value of the character at the given index.
concat()	Combines the text of two strings and returns a new string.
indexOf()	Returns the index within the calling String object of the first occurrence of the specified value, or -1 if not found.
lastIndexOf()	Returns the index within the calling String object of the last occurrence of the specified value, or -1 if not found.
localeCompare()	Returns a number indicating whether a reference string comes before or after or is the same as the given string in sort order.
length()	Returns the length of the string.
match()	Used to match a regular expression against a string.
replace()	Used to find a match between a regular expression and a string, and to replace the matched substring with a new substring.
search()	Executes the search for a match between a regular expression and a specified string.
slice()	Extracts a section of a string and returns a new string.
split()	Splits a String object into an array of strings by separating the string into substrings.
substr()	Returns the characters in a string beginning at the specified location through the specified number of characters.
substring()	Returns the characters in a string between two indexes into the string.
toLocaleLowerCase()	The characters within a string are converted to lower case while respecting the current locale.
toLocaleUpperCase()	The characters within a string are converted to upper case while respecting the current locale.
toLowerCase()	Returns the calling string value converted to lower case.
toString()	Returns a string representing the specified object.
toUpperCase()	Returns the calling string value converted to uppercase.
valueOf()	Returns the primitive value of the specified object.

String HTML wrappers

Here is a list of each method which returns a copy of the string wrapped inside the appropriate HTML tag.

Method	Description
anchor()	Creates an HTML anchor that is used as a hypertext target.
big()	Creates a string to be displayed in a big font as if it were in a <big> tag.
blink()	Creates a string to blink as if it were in a <blink> tag.
bold()	Creates a string to be displayed as bold as if it were in a <b> tag.
fixed()	Causes a string to be displayed in fixed-pitch font as if it were in a <tt> tag
fontcolor()	Causes a string to be displayed in the specified color as if it were in a <font color="color"> tag.
fontsize()	Causes a string to be displayed in the specified font size as if it were in a <font size="size"> tag.
italics()	Causes a string to be italic, as if it were in an <i> tag.
link()	Creates an HTML hypertext link that requests another URL.
small()	Causes a string to be displayed in a small font, as if it were in a <small> tag.
strike()	Causes a string to be displayed as struck-out text, as if it were in a <strike> tag.
sub()	Causes a string to be displayed as a subscript, as if it were in a <sub> tag
sup()	Causes a string to be displayed as a superscript, as if it were in a <sup> tag

Array Methods

Here is a list of each method and its description.

Method	Description
concat()	Returns a new array comprised of this array joined with other array(s) and/or value(s).
every()	Returns true if every element in this array satisfies the provided testing function.
filter()	Creates a new array with all of the elements of this array for which the provided filtering function returns true.
forEach()	Calls a function for each element in the array.
indexOf()	Returns the first (least) index of an element within the array equal to the specified value, or -1 if none is found.
join()	Joins all elements of an array into a string.
lastIndexOf()	Returns the last (greatest) index of an element within the array equal to the specified value, or -1 if none is found.
map()	Creates a new array with the results of calling a provided function on every element in this array.
pop()	Removes the last element from an array and returns that element.
push()	Adds one or more elements to the end of an array and returns the new length of the array.
reduce()	Apply a function simultaneously against two values of the array (from left-to-right) as to reduce it to a single value.
reduceRight()	Apply a function simultaneously against two values of the array (from right-to-left) as to reduce it to a single value.
reverse()	Reverses the order of the elements of an array -- the first becomes the last, and the last becomes the first.
shift()	Removes the first element from an array and returns that element.
slice()	Extracts a section of an array and returns a new array.
some()	Returns true if at least one element in this array satisfies the provided testing function.
toSource()	Represents the source code of an object
sort()	Sorts the elements of an array.
splice()	Adds and/or removes elements from an array.
toString()	Returns a string representing the array and its elements.
unshift()	Adds one or more elements to the front of an array and returns the new length of the array.

Date Methods:

Here is a list of each method and its description.

Method	Description
Date()	Returns today's date and time
getDate()	Returns the day of the month for the specified date according to local time.
getDay()	Returns the day of the week for the specified date according to local time.
getFullYear()	Returns the year of the specified date according to local time.
getHours()	Returns the hour in the specified date according to local time.
getMilliseconds()	Returns the milliseconds in the specified date according to local time.
getMinutes()	Returns the minutes in the specified date according to local time.
getMonth()	Returns the month in the specified date according to local time.
getSeconds()	Returns the seconds in the specified date according to local time.
getTime()	Returns the numeric value of the specified date as the number of milliseconds since January 1, 1970, 00:00:00 UTC.
getTimezoneOffset()	Returns the time-zone offset in minutes for the current locale.
getUTCDate()	Returns the day (date) of the month in the specified date according to universal time.
getUTCDay()	Returns the day of the week in the specified date according to universal time.
getUTCFullYear()	Returns the year in the specified date according to universal time.
getUTCHours()	Returns the hours in the specified date according to universal time.
getUTCMilliseconds()	Returns the milliseconds in the specified date according to universal time.
getUTCMinutes()	Returns the minutes in the specified date according to universal time.
getUTCMonth()	Returns the month in the specified date according to universal time.
getUTCSeconds()	Returns the seconds in the specified date according to universal time.
getYear()	Deprecated - Returns the year in the specified date according to local time. Use getFullYear instead.
setDate()	Sets the day of the month for a specified date according to local time.
setFullYear()	Sets the full year for a specified date according to local time.
setHours()	Sets the hours for a specified date according to local time.
setMilliseconds()	Sets the milliseconds for a specified date according to local time.
setMinutes()	Sets the minutes for a specified date according to local time.
setMonth()	Sets the month for a specified date according to local time.
setSeconds()	Sets the seconds for a specified date according to local time.
setTime()	Sets the Date object to the time represented by a number of milliseconds since January 1, 1970, 00:00:00 UTC.
setUTCDate()	Sets the day of the month for a specified date according to universal time.
setUTCFullYear()	Sets the full year for a specified date according to universal time.
setUTCHours()	Sets the hour for a specified date according to universal time.
setUTCMilliseconds()	Sets the milliseconds for a specified date according to universal time.
setUTCMinutes()	Sets the minutes for a specified date according to universal time.
setUTCMonth()	Sets the month for a specified date according to universal time.
setUTCSeconds()	Sets the seconds for a specified date according to universal time.
setYear()	Deprecated - Sets the year for a specified date according to local time. Use setFullYear instead.
toDateString()	Returns the "date" portion of the Date as a human-readable string.
toGMTString()	Deprecated - Converts a date to a string, using the Internet GMT conventions. Use toUTCString instead.
toLocaleDateString()	Returns the "date" portion of the Date as a string, using the current locale's conventions.
toLocaleFormat()	Converts a date to a string, using a format string.
toLocaleString()	Converts a date to a string, using the current locale's conventions.
toLocaleTimeString()	Returns the "time" portion of the Date as a string, using the current locale's conventions.
toSource()	Returns a string representing the source for an equivalent Date object; you can use this value to create a new object.
toString()	Returns a string representing the specified Date object.
toTimeString()	Returns the "time" portion of the Date as a human-readable string.
toUTCString()	Converts a date to a string, using the universal time convention.
valueOf()	Returns the primitive value of a Date object.

Date Static Methods:

In addition to the many instance methods listed previously, the Date object also defines two static methods. These methods are invoked through the Date( ) constructor itself:

Method	Description
Date.parse( )	Parses a string representation of a date and time and returns the internal millisecond representation of that date.
Date.UTC( )	Returns the millisecond representation of the specified UTC date and time.

Math Methods

Here is a list of each method and its description.

Method	Description
abs()	Returns the absolute value of a number.
acos()	Returns the arccosine (in radians) of a number.
asin()	Returns the arcsine (in radians) of a number.
atan()	Returns the arctangent (in radians) of a number.
atan2()	Returns the arctangent of the quotient of its arguments.
ceil()	Returns the smallest integer greater than or equal to a number.
cos()	Returns the cosine of a number.
exp()	Returns E^N, where N is the argument, and E is Euler's constant, the base of the natural logarithm.
floor()	Returns the largest integer less than or equal to a number.
log()	Returns the natural logarithm (base E) of a number.
max()	Returns the largest of zero or more numbers.
min()	Returns the smallest of zero or more numbers.
pow()	Returns base to the exponent power, that is, base exponent.
random()	Returns a pseudo-random number between 0 and 1.
round()	Returns the value of a number rounded to the nearest integer.
sin()	Returns the sine of a number.
sqrt()	Returns the square root of a number.
tan()	Returns the tangent of a number.
toSource()	Returns the string "Math".

RegExp Methods:

Here is a list of each method and its description.

Method	Description
exec()	Executes a search for a match in its string parameter.
test()	Tests for a match in its string parameter.
toSource()	Returns an object literal representing the specified object; you can use this value to create a new object.
toString()	Returns a string representing the specified object.

What is an Event ?

JavaScript's interaction with HTML is handled through events that occur when the user or browser manipulates a page.

When the page loads, that is an event. When the user clicks a button, that click, too, is an event. Another example of events are like pressing any key, closing window, resizing window etc.

Developers can use these events to execute JavaScript coded responses, which cause buttons to close windows, messages to be displayed to users, data to be validated, and virtually any other type of response imaginable to occur.

Events are a part of the Document Object Model (DOM) Level 3 and every HTML element have a certain set of events which can trigger JavaScript Code.

Please go through this small tutorial for a better understanding HTML Event Reference. Here we will see few examples to understand a relation between Event and JavaScript:

onclick Event Type:

This is the most frequently used event type which occurs when a user clicks mouse left button. You can put your validation, warning etc against this event type.

Example:

<html>

<head>

<!--

function sayHello() {

alert("Hello World")

}

//-->

</script>

</head>

<body>

</body>

</html>

This will produce following result and when you click Hello button then onclick event will occur which will trigger sayHello() function.

onsubmit event type:

Another most important event type is onsubmit. This event occurs when you try to submit a form. So you can put your form validation against this event type.

Here is simple example showing its usage. Here we are calling a validate() function before submitting a form data to the webserver. If validate() function returns true the form will be submitted otherwise it will not submit the data.

Example:

<html>

<head>

<!--

function validation() {

all validation goes here

.........

return either true or false

}

//-->

</script>

</head>

<body>

.......

</form>

</body>

</html>

onmouseover and onmouseout:

These two event types will help you to create nice effects with images or even with text as well. The onmouseover event occurs when you bring your mouse over any element and theonmouseout occurs when you take your mouse out from that element.

Example:

Following example shows how a division reacts when we bring our mouse in that division:

<html>

<head>

<!--

function over() {

alert("Mouse Over");

}

function out() {

alert("Mouse Out");

}

//-->

</script>

</head>

<body>

<h2> This is inside the division </h2>

</div>

</body>

</html>

You can change different images using these two event types or you can create help baloon to help your users.

HTML 4 Standard Events

The standard HTML 4 events are listed here for your reference. Here script indicates a Javascript function to be executed agains that event.

Event	Value	Description
onchange	script	Script runs when the element changes
onsubmit	script	Script runs when the form is submitted
onreset	script	Script runs when the form is reset
onselect	script	Script runs when the element is selected
onblur	script	Script runs when the element loses focus
onfocus	script	Script runs when the element gets focus
onkeydown	script	Script runs when key is pressed
onkeypress	script	Script runs when key is pressed and released
onkeyup	script	Script runs when key is released
onclick	script	Script runs when a mouse click
ondblclick	script	Script runs when a mouse double-click
onmousedown	script	Script runs when mouse button is pressed
onmousemove	script	Script runs when mouse pointer moves
onmouseout	script	Script runs when mouse pointer moves out of an element
onmouseover	script	Script runs when mouse pointer moves over an element
onmouseup	script	Script runs when mouse button is released

What are Cookies ?

Web Browser and Server use HTTP protocol to communicate and HTTP is a stateless protocol. But for a commercial website it is required to maintain session information among different pages. For example one user registration ends after completing many pages. But how to maintain user's session information across all the web pages.

In many situations, using cookies is the most efficient method of remembering and tracking preferences, purchases, commissions, and other information required for better visitor experience or site statistics.

How It Works ?

Your server sends some data to the visitor's browser in the form of a cookie. The browser may accept the cookie. If it does, it is stored as a plain text record on the visitor's hard drive. Now, when the visitor arrives at another page on your site, the browser sends the same cookie to the server for retrieval. Once retrieved, your server knows/remembers what was stored earlier.

Cookies are a plain text data record of 5 variable-length fields:

Expires : The date the cookie will expire. If this is blank, the cookie will expire when the visitor quits the browser.
Domain : The domain name of your site.
Path : The path to the directory or web page that set the cookie. This may be blank if you want to retrieve the cookie from any directory or page.
Secure : If this field contains the word "secure" then the cookie may only be retrieved with a secure server. If this field is blank, no such restriction exists.
Name=Value : Cookies are set and retrieved in the form of key and value pairs.

Cookies were originally designed for CGI programming and cookies' data is automatically transmitted between the web browser and web server, so CGI scripts on the server can read and write cookie values that are stored on the client.

JavaScript can also manipulate cookies using the cookie property of the Document object. JavaScript can read, create, modify, and delete the cookie or cookies that apply to the current web page.

Storing Cookies:

The simplest way to create a cookie is to assign a string value to the document.cookie object, which looks like this:

Syntax:

document.cookie = "key1=value1;key2=value2;expires=date";

Here expires attribute is option. If you provide this attribute with a valid date or time then cookie will expire at the given date or time and after that cookies' value will not be accessible.

Note: Cookie values may not include semicolons, commas, or whitespace. For this reason, you may want to use the JavaScript escape() function to encode the value before storing it in the cookie. If you do this, you will also have to use the corresponding unescape() function when you read the cookie value.

Example:

Following is the example to set a customer name in input cookie.

<html>

<head>

<!--

function WriteCookie()

{

if( document.myform.customer.value == "" ){

alert("Enter some value!");

return;

}

cookievalue= escape(document.myform.customer.value) + ";";

document.cookie="name=" + cookievalue;

alert("Setting Cookies : " + "name=" + cookievalue );

}

//-->

</script>

</head>

<body>

Enter name: <input type="text" name="customer"/>

</form>

</body>

</html>

This will produce following result. Now enter something in the text box and press the button "Set Cookie" to set the cookies.

Enter name:

Now your machine has a cookie called name. You can set multiple cookies using multiplekey=value pairs separated by comma.

You will learn how to read this cookie in next section.

Reading Cookies:

Reading a cookie is just as simple as writing one, because the value of the document.cookieobject is the cookie. So you can use this string whenever you want to access the cookie.

The document.cookie string will keep a list of name=value pairs separated by semicolons, wherename is the name of a cookie and value is its string value.

You can use strings' split() function to break the string into key and values as follows:

Example:

Following is the example to get the cookies set in previous section.

<html>

<head>

<!--

function ReadCookie()

{

var allcookies = document.cookie;

alert("All Cookies : " + allcookies );

// Get all the cookies pairs in an array

cookiearray = allcookies.split(';');

// Now take key value pair out of this array

for(var i=0; i<cookiearray.length; i++){

name = cookiearray[i].split('=')[0];

value = cookiearray[i].split('=')[1];

alert("Key is : " + name + " and Value is : " + value);

}

//-->

</script>

</head>

<body>

</form>

</body>

</html>

Note: Here length is a method of Array class which returns the length of an array. We will discuss Arrays in a separate chapter. By that time please try to digest it.

This will produce following result. Now press the button "Get Cookie" to see the cookies which you have set in previous section.

Note: There may be some other cookies already set on your machine. So above code will show you all the cookies set at your machine.

Setting the Cookies Expiration Date:

You can extend the life of a cookie beyond the current browser session by setting an expiration date and saving the expiration date within the cookie. This can be done by setting the expiresattribute to a date and time.

Example:

The following example illustrates how to set cookie expiration date after 1 Month :

<html>

<head>

<!--

function WriteCookie()

{

var now = new Date();

now.setMonth( now.getMonth() + 1 );

cookievalue = escape(document.myform.customer.value) + ";"

document.cookie="name=" + cookievalue;

document.cookie = "expires=" + now.toUTCString() + ";"

alert("Setting Cookies : " + "name=" + cookievalue );

}

//-->

</script>

</head>

<body>

Enter name: <input type="text" name="customer"/>

</form>

</body>

</html>

Deleting a Cookie:

Sometimes you will want to delete a cookie so that subsequent attempts to read the cookie return nothing. To do this, you just need to set the expiration date to a time in the past.

Example:

The following example illustrates how to delete cookie by setting expiration date one Month in past :

<html>

<head>

<!--

function WriteCookie()

{

var now = new Date();

now.setMonth( now.getMonth() - 1 );

cookievalue = escape(document.myform.customer.value) + ";"

document.cookie="name=" + cookievalue;

document.cookie = "expires=" + now.toUTCString() + ";"

alert("Setting Cookies : " + "name=" + cookievalue );

}

//-->

</script>

</head>

<body>

Enter name: <input type="text" name="customer"/>

</form>

</body>

</html>

Note: Instead of setting date, you can see new time using setTime() function.

JavaScript is an Object Oriented Programming (OOP) language. A programming language can be called object-oriented if it provides four basic capabilities to developers:

Encapsulation . the capability to store related information, whether data or methods, together in an object
Aggregation . the capability to store one object inside of another object
Inheritance . the capability of a class to rely upon another class (or number of classes) for some of its properties and methods
Polymorphism . the capability to write one function or method that works in a variety of different ways

Objects are composed of attributes. If an attribute contains a function, it is considered to be a method of the object otherwise, the attribute is considered a property.

Object Properties:

Object properties can be any of the three primitive data types, or any of the abstract data types, such as another object. Object properties are usually variables that are used internally in the object's methods, but can also be globally visible variables that are used throughout the page.

The syntax for adding a property to an object is:

objectName.objectProperty = propertyValue;

Example:

Following is a simple example to show how to get a document title using "title" property of document object:

var str = document.title;

Object Methods:

The methods are functions that let the object do something or let something be done to it. There is little difference between a function and a method, except that a function is a standalone unit of statements and a method is attached to an object and can be referenced by the this keyword.

Methods are useful for everything from displaying the contents of the object to the screen to performing complex mathematical operations on a group of local properties and parameters.

Example:

Following is a simple example to show how to use write() method of document object to write any content on the document:

document.write("This is test");

User-Defined Objects:

All user-defined objects and built-in objects are descendants of an object called Object.

The new Operator:

The new operator is used to create an instance of an object. To create an object, the newoperator is followed by the constructor method.

In the following example, the constructor methods are Object(), Array(), and Date(). These constructors are built-in JavaScript functions.

var employee = new Object();

var books = new Array("C++", "Perl", "Java");

var day = new Date("August 15, 1947");

The Object() Constructor:

A constructor is a function that creates and initializes an object. JavaScript provides a special constructor function called Object() to build the object. The return value of the Object() constructor is assigned to a variable.

The variable contains a reference to the new object. The properties assigned to the object are not variables and are not defined with the var keyword.

Example 1:

This example demonstrates how to create an object:

<html>

<head>

<title>User-defined objects</title>

var book = new Object(); // Create the object

book.subject = "Perl"; // Assign properties to the object

book.author = "Mohtashim";

</script>

</head>

<body>

document.write("Book name is : " + book.subject + "<br>");

document.write("Book author is : " + book.author + "<br>");

</script>

</body>

</html>

Example 2:

This example demonstrates how to create an object with a User-Defined Function. Here thiskeyword is used to refer to the object that has been passed to a function:

<html>

<head>

<title>User-defined objects</title>

function book(title, author){

this.title = title;

this.author = author;

}

</script>

</head>

<body>

var myBook = new book("Perl", "Mohtashim");

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

</script>

</body>

</html>

Defining Methods for an Object:

The previous examples demonstrate how the constructor creates the object and assigns properties. But we need to complete the definition of an object by assigning methods to it.

Example:

Here is a simple example to show how to add a function along with an object:

<html>

<head>

<title>User-defined objects</title>

// Define a function which will work as a method

function addPrice(amount){

this.price = amount;

}

function book(title, author){

this.title = title;

this.author = author;

this.addPrice = addPrice; // Assign that method as property.

}

</script>

</head>

<body>

var myBook = new book("Perl", "Mohtashim");

myBook.addPrice(100);

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

document.write("Book price is : " + myBook.price + "<br>");

</script>

</body>

</html>

The with Keyword:

The with keyword is used as a kind of shorthand for referencing an object's properties or methods.

The object specified as an argument to with becomes the default object for the duration of the block that follows. The properties and methods for the object can be used without naming the object.

Syntax:

with (object){

properties used without the object name and dot

}

Example:

<html>

<head>

<title>User-defined objects</title>

// Define a function which will work as a method

function addPrice(amount){

with(this){

price = amount;

}

function book(title, author){

this.title = title;

this.author = author;

this.price = 0;

this.addPrice = addPrice; // Assign that method as property.

}

</script>

</head>

<body>

var myBook = new book("Perl", "Mohtashim");

myBook.addPrice(100);

document.write("Book title is : " + myBook.title + "<br>");

document.write("Book author is : " + myBook.author + "<br>");

document.write("Book price is : " + myBook.price + "<br>");

</script>

</body>

</html>

JavaScript Native Objects:

JavaScript has several built-in or native objects. These objects are accessible anywhere in your program and will work the same way in any browser running in any operating system.

Here is the list of all important JavaScript Native Objects:

There are three types of errors in programming: (a) Syntax Errors and (b) Runtime Errors (c) Logical Errors:

Syntax errors:

Syntax errors, also called parsing errors, occur at compile time for traditional programming languages and at interpret time for JavaScript.

For example, the following line causes a syntax error because it is missing a closing parenthesis:

<!--

window.print(;

//-->

</script>

When a syntax error occurs in JavaScript, only the code contained within the same thread as the syntax error is affected and code in other threads gets executed assuming nothing in them depends on the code containing the error.

Runtime errors:

Runtime errors, also called exceptions, occur during execution (after compilation/interpretation).

For example, the following line causes a run time error because here syntax is correct but at run time it is trying to call a non existed method:

<!--

window.printme();

//-->

</script>

Exceptions also affect the thread in which they occur, allowing other JavaScript threads to continue normal execution.

Logical errors:

Logic errors can be the most difficult type of errors to track down. These errors are not the result of a syntax or runtime error. Instead, they occur when you make a mistake in the logic that drives your script and you do not get the result you expected.

You can not catch those errors, because it depends on your business requirement what type of logic you want to put in your program.

The try...catch...finally Statement:

The latest versions of JavaScript added exception handling capabilities. JavaScript implements the try...catch...finally construct as well as the throw operator to handle exceptions.

You can catch programmer-generated and runtime exceptions, but you cannot catch JavaScript syntax errors.

Here is the try...catch...finally block syntax:

<!--

try {

// Code to run

[break;]

} catch ( e ) {

// Code to run if an exception occurs

[break;]

}[ finally {

// Code that is always executed regardless of

// an exception occurring

}]

//-->

</script>

The try block must be followed by either exactly one catch block or one finally block (or one of both). When an exception occurs in the try block, the exception is placed in e and the catchblock is executed. The optional finally block executes unconditionally after try/catch.

Examples:

Here is one example where we are trying to call a non existing function this is causing an exception raise. Let us see how it behaves without with try...catch:

<html>

<head>

<!--

function myFunc()

{

var a = 100;

alert("Value of variable a is : " + a );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

Now let us try to catch this exception using try...catch and display a user friendly message. You can also suppress this message, if you want to hide this error from a user.

<html>

<head>

<!--

function myFunc()

{

var a = 100;

try {

alert("Value of variable a is : " + a );

} catch ( e ) {

alert("Error: " + e.description );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

You can use finally block which will always execute unconditionally after try/catch. Here is an example:

<html>

<head>

<!--

function myFunc()

{

var a = 100;

try {

alert("Value of variable a is : " + a );

}catch ( e ) {

alert("Error: " + e.description );

}finally {

alert("Finally block will always execute!" );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

The throw Statement:

You can use throw statement to raise your built-in exceptions or your customized exceptions. Later these exceptions can be captured and you can take an appropriate action.

Following is the example showing usage of throw statement.

<html>

<head>

<!--

function myFunc()

{

var a = 100;

var b = 0;

try{

if ( b == 0 ){

throw( "Divide by zero error." );

}else{

var c = a / b;

}

}catch ( e ) {

alert("Error: " + e );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

You can raise an exception in one function using a string, integer, Boolean or an object and then you can capture that exception either in the same function as we did above, or in other function using try...catch block.

The onerror() Method

The onerror event handler was the first feature to facilitate error handling for JavaScript. Theerror event is fired on the window object whenever an exception occurs on the page. Example:

<html>

<head>

<!--

window.onerror = function () {

alert("An error occurred.");

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

The onerror event handler provides three pieces of information to identify the exact nature of the error:

Error message . The same message that the browser would display for the given error
URL . The file in which the error occurred
Line number . The line number in the given URL that caused the error

Here is the example to show how to extract this information

<html>

<head>

<!--

window.onerror = function (msg, url, line) {

alert("Message : " + msg );

alert("url : " + url );

alert("Line number : " + line );

}

//-->

</script>

</head>

<body>

<p>Click the following to see the result:</p>

<form>

</form>

</body>

</html>

You can display extracted information in whatever way you think it is better.

You can use onerror method to show an error message in case there is any problem in loading an image as follows:

<img src="myimage.gif"

onerror="alert('An error occurred loading the image.')" />

You can use onerror with many HTML tags to display appropriate messages in case of errors.

JavaScript - Form Validation

Form validation used to occur at the server, after the client had entered all necessary data and then pressed the Submit button. If some of the data that had been entered by the client had been in the wrong form or was simply missing, the server would have to send all the data back to the client and request that the form be resubmitted with correct information. This was really a lengthy process and over burdening server.

JavaScript, provides a way to validate form's data on the client's computer before sending it to the web server. Form validation generally performs two functions.

Basic Validation - First of all, the form must be checked to make sure data was entered into each form field that required it. This would need just loop through each field in the form and check for data.
Data Format Validation - Secondly, the data that is entered must be checked for correct form and value. This would need to put more logic to test correctness of data.

We will take an example to understand the process of validation. Here is the simple form to proceed :

<html>

<head>

<title>Form Validation</title>

<!--

// Form validation code will come here.

//-->

</script>

</head>

<body>

<form action="/cgi-bin/test.cgi" name="myForm"

onsubmit="return(validate());">

<tr>

</tr>

<tr>

<td align="right">EMail</td>

</tr>

<tr>

</tr>

<tr>

<td align="right">Country</td>

<td>

<option value="-1" selected>[choose yours]</option>

<option value="3">INDIA</option>

</select>

</td>

</tr>

<tr>

</tr>

</table>

</form>

</body>

</html>

Basic Form Validation:

First we will show how to do a basic form validation. In the above form we are calling validate()function to validate data when onsubmit event is occurring. Following is the implementation of this validate() function:

<!--

// Form validation code will come here.

function validate()

{

if( document.myForm.Name.value == "" )

{

alert( "Please provide your name!" );

document.myForm.Name.focus() ;

return false;

}

if( document.myForm.EMail.value == "" )

{

alert( "Please provide your Email!" );

document.myForm.EMail.focus() ;

return false;

}

if( document.myForm.Zip.value == "" ||

isNaN( document.myForm.Zip.value ) ||

document.myForm.Zip.value.length != 5 )

{

alert( "Please provide a zip in the format #####." );

document.myForm.Zip.focus() ;

return false;

}

if( document.myForm.Country.value == "-1" )

{

alert( "Please provide your country!" );

return false;

}

return( true );

}

//-->

</script>

Data Format Validation:

Now we will see how we can validate our entered form data before submitting it to the web server.

This example shows how to validate an entered email address which means email address must contain at least an @ sign and a dot (.). Also, the @ must not be the first character of the email address, and the last dot must at least be one character after the @ sign:

<!--

function validateEmail()

{

var emailID = document.myForm.EMail.value;

atpos = emailID.indexOf("@");

dotpos = emailID.lastIndexOf(".");

if (atpos < 1 || ( dotpos - atpos < 2 ))

{

alert("Please enter correct email ID")

document.myForm.EMail.focus() ;

return false;

}

return( true );

}

//-->

</script>

Javascript Animation

You can use JavaScript to create a complex animation which includes but not limited to:

Fireworks
Fade Effect
Roll-in or Roll-out
Page-in or Page-out
Object movements

You might be interested in existing JavaScript based animation library : Script.Aculo.us.

This tutorial will give you basic understanding on how to use JavaScript to create an animation.

JavaScript can be used to move a number of DOM elements (<img />, <div> or any other HTML element) around the page according to some sort of pattern determined by a logical equation or function.

JavaScript provides following two functions to be frequently used in animation programs.

setTimeout( function, duration) - This function calls function after durationmilliseconds from now.
setInterval(function, duration) - This function calls function after every durationmilliseconds.
clearTimeout(setTimeout_variable) - This function calls clears any timer set by the setTimeout() functions.

JavaScript can also set a number of attributes of a DOM object including its position on the screen. You can set top and left attribute of an object to position it anywhere on the screen. Here is the simple syntax:

// Set distance from left edge of the screen.

object.style.left = distance in pixels or points;

// Set distance from top edge of the screen.

object.style.top = distance in pixels or points;

Manual Animation:

So let's implement one simple animation using DOM object properties and JavaScript functions as follows:

<html>

<head>

<title>JavaScript Animation</title>

<!--

var imgObj = null;

function init(){

imgObj = document.getElementById('myImage');

imgObj.style.position= 'relative';

imgObj.style.left = '0px';

}

function moveRight(){

imgObj.style.left = parseInt(imgObj.style.left) + 10 + 'px';

}

window.onload =init;

//-->

</script>

</head>

<body>

<form>

<p>Click button below to move the image to right</p>

</form>

</body>

</html>

Here is the explanation of the above example:

We are using JavaScript function getElementById() to get a DOM object and then assigning it to a global variable imgObj.
We have defined an initialization function init() to initialize imgObj where we have set itsposition and left attributes.
We are calling initialization function at the time of window load.
Finally, we are calling moveRight() function to increase left distance by 10 pixels. You could also set it to a negative value to move it to the left side.

Automated Animation:

In the above example we have seen , how an image moves to right with every click. We can automate this process by using JavaScript function setTimeout() as follows:

<html>

<head>

<title>JavaScript Animation</title>

<!--

var imgObj = null;

var animate ;

function init(){

imgObj = document.getElementById('myImage');

imgObj.style.position= 'relative';

imgObj.style.left = '0px';

}

function moveRight(){

imgObj.style.left = parseInt(imgObj.style.left) + 10 + 'px';

animate = setTimeout(moveRight,20); // call moveRight in 20msec

}

function stop(){

clearTimeout(animate);

imgObj.style.left = '0px';

}

window.onload =init;

//-->

</script>

</head>

<body>

<form>

<p>Click the buttons below to handle animation</p>

</form>

</body>

</html>

Here we have add more spice. So let's see what is new here:

The moveRight() function is calling setTimeout() function to set the position of imgObj.
We have added a new function stop() to clear the timer set by setTimeout() function and to set the object at its initial position.

Rollover with a Mouse Event:

Here is a simple example showing image rollover with a mouse events:

<html>

<head>

<title>Rollover with a Mouse Events</title>

<!--

if(document.images){

var image1 = new Image(); // Preload an image

image1.src = "/images/html.gif";

var image2 = new Image(); // Preload second image

image2.src = "/images/http.gif";

}

//-->

</script>

</head>

<body>

<p>Move your mouse over the image to see the result</p>

<a href="#" onMouseOver="document.myImage.src=image2.src;"

onMouseOut="document.myImage.src=image1.src;">

</a>

</body>

</html>

Let's see what is different here:

At the time of loading this page, the if statement checks for the existence of the image object. If the image object is unavailable, this block will not be executed.
The Image() constructor creates and preloads a new image object called image1.
The src property is assigned the name of the external image file called /images/html.gif.
Similar way we have created image2 object and assigned /images/http.gif in this object.
The # (hash mark) disables the link so that the browser does not try to go to a URL when clicked. This link is an image.
The onMouseOver event handler is triggered when the user's mouse moves onto the link, and the onMouseOut event handler is triggered when the user's mouse moves away from the link (image).
When the mouse moves over the image, the HTTP image changes from the first image to the second one. When the mouse is moved away from the image, the original image is displayed.
When the mouse is moved away from the link, the initial image html.gif will reappear on the screen.

Thursday 21 March 2013