JavaScript Variable

A JavaScript variable is simply a name of storage location. There are two types of variables in JavaScript : local variable and global variable.

There are some rules while declaring a JavaScript variable (also known as identifiers).

1. Name must start with a letter (a to z or A to Z), underscore( _ ), or dollar( $ ) sign.
2. After first letter we can use digits (0 to 9), for example value1.
3. JavaScript variables are case sensitive, for example x and X are different variables.

Correct JavaScript variables

var x = 10;  

var _value="sonoo";

Incorrect JavaScript variables

Example of JavaScript variable

Let’s see a simple example of JavaScript variable.

var  123=30;  

var *aa=320;

<script>  

var x = 10;  

var y = 20;  

var z=x+y;  

document.write(z);  

</script>

Output of the above example

30

JavaScript local variable

A JavaScript local variable is declared inside block or function. It is accessible within the function or block only. For example:

<script>  
function abc(){  
var x=10;//local variable  
}  
</script>  

Or,

<script>  

If(10<13){  

var y=20;//JavaScript local variable  

}  

</script>

JavaScript global variable

A JavaScript 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. For example:

<script>  

var data=200;//gloabal variable  

function a(){  

document.writeln(data);  

}  

function b(){  

document.writeln(data);  

}  

a();//calling JavaScript function  

b();  

</script