JavaScript Variable

A variable is simply a container that stores a value in a location. This value can be changed during the execution of the program. There are two types of variable.

1. Local Variable:- A variable is declared within the function or inside the block. It is accessible within the function or block only.
   
   <script>
   function abc()
   {
   variable x = 10:// local variable
   }
   </script>
2. Global Variable:– A variable is declared outside of any function or declared with a window object.
   
   <script>
   var data = 200://global variable
   function a () {
   }
   </script>
   
   

Rules for declaring a variable name

1. The name must start with a letter ( a to z or A to Z), underscore (_), or dollar sign ($)
2. After the first letter, we can use digits (0 to 9)
3. Variables are case-sensitive (ex:- harry and Harry are different)
4. White space not allowed (ex:- int code with Harry; is invalid)
5. let can be updated but not re-declared
6. Constant can neither be updated nor be re-declared.
7. Variables are initialized with undefined whereas let and constant variables are not initialized.