Variable In JavaScript

Variable means whose value can be changed.

Variable contains value which is stored in memory and holds some space.

var keyword is used to declare a variable in javascript.

2 steps to use variables

·        Variable Declaration

·        Variable Initialization

   Variable Declaration:

Syntax: 

var variable_name;

Eg 1:

var x;

Where x is the variable name.

Variable Initialization:

Syntax:

var variablename=value;

 Eg 1:

var x=89;

Where x is the variable name and 89 is the value which assigned to x.

 

Rules for defining variables

It can have alphabets, digits and underscore  or dollar( $ ) sign.

A variable name should start with alphabet and underscore only. It can't start with digit.

No white space is allowed within variable name.

JavaScript variables are case sensitive, for example y and Y are different variables.

 

Valid variable declaration:
int x;    

     int _xy;    

      int x45;    

Invalid variable declaration:
 int 7;   
 int *bb  

Example:

   <script>  

   var x = 20;  

  document.write(x);  

  </script>

Types:

There are two types of variables in JavaScript ,they are

 1)local variable

 2)global variable

Local variable:

local variable is declared inside block or function. It is accessible within the function or block only.

Example:

    <script>  

   function display (){  

   var x=20;//local variable 

    document.write("x is:"+x);   

      } 

    display();

    </script>  

    

    global variable

global variable is accessible from any function. A variable i.e. declared outside the function or declared with window object is known as global variable.

Example:

<script>  

var x=30;//global variable  

     function display(){  

     document.write("x is:"+x);    

        }  

    display();

  </script>