What is a JavaScript Variable?

Define JavaScript Variable

JavaScript variable are containers, It is a way to store/contain data(information) value in memory , so that you can reference and use it later and multiple time in the program.

In JavaScript creating a variable is called "declaring" a variable.

A variable name must have a unique name. You can assign a value to a variable using assignment(=) operator when you declare it or before using it.

In JavaScript, there are 3-reserved keywords used to declare a variable :— let, var, and const.

1. Using var.

2. Using let.

3. Using const.

Note : JavaScript is a dynamically typed language. This means that a JavaScript variable can hold a value of any data type.

Important point of JavaScript variable :

• You cannot access the JavaScript variable before you define it.

 ➤ Example :

<script>
     console.log(myName); //Uncaught ReferenceError: myName is not defined
     const myName = 'Ankaj Gupta';
 </script>

Output :

ReferenceError: can't access lexical declaration `myName' before initialization

• Javascript variables are dynamic typing mean that, they can change from one data type to another data type.

 ➤ Example :

    In this example, the variable myName change from string to number and then boolean.

<script>
     var myName = 'Ankaj Gupta';  //Ankaj Gupta
     myName = 100;   //100  
     myName = true;  //true
 </script>

• JavaScript allows multiple line breaks and white spaces when you declare a variable with var keyword.

 ➤ Example : Whitespace and Line Breaks

Please note that semicolon is optional.

<script>
     var
             one
         =

         1,
            two
            =
            "two"
 </script>

• JavaScript variables are loosely typed, means that a variable can hold a value with any type of data. It does't require a data type to be declared, you can assign any type of literal values to a variable e.g : string, integer, float, boolean etc.

 ➤ Example : Loosely typed variables

<script>
   var one =1;  // Numeric value
   one = 'one'; // String value
   one= 1.1; // Decimal value
   one = null; // null value
   one = true; // Boolean value
 </script>