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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

  1. var x = 10;
  2. var _value=“sonoo”;

Incorrect JavaScript variables

  1. var  123=30;
  2. var *aa=320;

Example of JavaScript variable

Let’s see a simple example of JavaScript variable.

  1. <script>
  2. var x = 10;
  3. var y = 20;
  4. var z=x+y;
  5. document.write(z);
  6. </script>

Test it Now

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:

  1. <script>
  2. function abc(){
  3. var x=10;//local variable
  4. }
  5. </script>

Or,

  1. <script>
  2. If(10<13){
  3. var y=20;//JavaScript local variable
  4. }
  5. </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:

  1. <script>
  2. var data=200;//gloabal variable
  3. function a(){
  4. document.writeln(data);
  5. }
  6. function b(){
  7. document.writeln(data);
  8. }
  9. a();//calling JavaScript function
  10. b();
  11. </script>

Test it Now

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

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