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JavaScript variable

JavaScript variable tutorial for beginners and professionals with example, local variable, global variable, example, event, validation, object loop, array, document, tutorial

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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

var  123=30;
var *aa=320;

Example of JavaScript variable

Let’s see a simple example of JavaScript variable.

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

Output of the above example

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>
Test it Now

To know more about global variable (e.g. how global variable is executed by JavaScript execution engine), visit next page.

Next TopicJavaScript Global Variable




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