JavaScript Variable

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>  

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>