JAVA SCRIPT

JavaScript

• JavaScript was designed to add interactivity to HTML pages
• JavaScript is a scripting language
• A scripting language is a lightweight programming language
• JavaScript is usually embedded directly into HTML pages
• JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
• Everyone can use JavaScript without purchasing a license

• JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
• JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("name ") can write a variable text into an HTML page
• JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
• JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
• JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
• JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
• JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer
  

· JavaScript's official name is ECMAScript.

· ECMAScript is developed and maintained by the ECMA organization.

· ECMA-262 is the official JavaScript standard.

· The language was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all Netscape and Microsoft browsers since 1996.

· The development of ECMA-262 started in 1996, and the first edition of was adopted by the ECMA General Assembly in June 1997.

· The standard was approved as an international ISO (ISO/IEC 16262) standard in 1998.

· The development of the standard is still in progress.

script type="text/javascript" src="xxx.js"

JavaScript is Case Sensitive

JavaScript Statements

A JavaScript statement is a command to a browser. The purpose of the command is to tell the browser what to do.

document.write("Hello Dolly");

Note: Using semicolons makes it possible to write multiple statements on one line.

JavaScript code (or just JavaScript) is a sequence of JavaScript statements.

Each statement is executed by the browser in the sequence they are written.

JavaScript statements can be grouped together in blocks.

Blocks start with a left curly bracket {, and ends with a right curly bracket }.

The purpose of a block is to make the sequence of statements execute together.

JavaScript Comments

Single line comments start with //.

Multi line comments start with /* and end with */.

Using Comments to Prevent Execution

JavaScript Variables

Rules for JavaScript variable names:

• Variable names are case sensitive (y and Y are two different variables)
• Variable names must begin with a letter or the underscore character

You can declare JavaScript variables with the var statement: var x; var carname;

var x=5; var carname="Volvo";

*If you redeclare a JavaScript variable, it will not lose its original value.

JavaScript Operators

= is used to assign values.

+ is used to add values.

JavaScript Arithmetic Operators

Operator	Description	Example	Result
+	Addition	x=y+2	x=7
-	Subtraction	x=y-2	x=3
*	Multiplication	x=y*2	x=10
/	Division	x=y/2	x=2.5
%	Modulus (division remainder)	x=y%2	x=1
++	Increment	x=++y	x=6
--	Decrement	x=--y	x=4

JavaScript Assignment Operators

Operator	Example	Same As	Result
=	x=y		x=5
+=	x+=y	x=x+y	x=15
-=	x-=y	x=x-y	x=5
*=	x*=y	x=x*y	x=50
/=	x/=y	x=x/y	x=2
%=	x%=y	x=x%y	x=0

Comparison Operators

Operator	Description	Example
=	is equal to	x= 8 is false
= =	is exactly equal to (value and type)	x= = 5 is true x= = "5" is false
!=	is not equal	x!=8 is true
	is greater than	x>8 is false
<	is less than	x<8>
>=	is greater than or equal to	x>=8 is false
<=	is less than or equal to	x<=8 is true

Logical Operators

Operator	Description	Example
&&	and	(x <> 1) is true
||	or	(x= =5 || y= =5) is false
!	not	!(x= =y) is true

Conditional Operator

Syntax

variablename=(condition)?value1:value2

Example

greeting=(visitor=="PRES")?"Dear President ":"Dear ";