Learn JavaScript for Web Development

JavaScript is most versatile languages to code applications for the browser, desktop, phone or tablet. Write program for client browser or web server. Build interactive web site with JavaScript.

JavaScript Variables

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

var 123=30; var *aa=320;

Example of JavaScript variable

Let’s see a simple example of JavaScript variable.

See this example:

<script> var x = 10; var y = 20; var z=x+y; document.write(z); </script>


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>


<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>