JavaScript Variables

By | October 1, 2021
JavaScript Variables Tutorial

What are Variables in JavaScript

When we write the JavaScript code we deal with many types of data it could be a number, name, date, speed value, etc., and to use these values we require variables.

A variable is a data container or storage which holds the data value for us. To create a variable in JavaScript we write the variable name followed by the assignment operator = and the variable value.


name = 'Rahul';
var name = 'Rahul';
let name ='Rahul';

All three statements can be used to create or declare a variable in JavaScript. In the above JavaScript code name is the variable, =  symbol is assignment operator and 'Rahul' is the data value.

As JavaScript is a loosely typed language, you can or cannot use semicolon ; at the end of statements.

The let and var are the JavaScript keywords which we will be going to discuss in another tutorial.

What are Constants in JavaScript?

Constants are the special variables, a normal variable can be declared with or without keywords like var and let and their value can be changed throughout the program.


But a constant variable is defined with const keyword and its value remains the same throughout the program and if you try to change it, the JavaScript engine or interpreter will throw an error.


const name2 = "Ravi";    //constant variable 

name2= "Raghav";   // error

JavaScript Variable Naming Rules

We can not give any name to the variables, there are some set of rules we need to follow when we give a name to our variable.

Rule 1: A Variable name can only start with alphabets, $ (dollar) or _ (underscore) symbol.

Name1 = "Rahul";      //valid
name1 = "Rahul";      //valid
&name = "Rahul";      // valid
_name = "Rahul";      // valid
1name = "Rahul";      // invalid
&name = "Rahul";      // Invalid

Rule 2:  A reserved JavaScript Keyword can not be used as a variable name. There are 63 reserved keywords in JavaScript.

let let = "Rahul";  // invalid
var let = "Rahul";  // invalid

Rule 3: A variable name must be a sequence of alphabets, numbers, underscore, and $ dollar symbol.

name$_12 = "Rahul";    //valid 
name&_12 = "Rahul";    // invalid

Rule 4: There must not be any space or gap in the variable name.

name 1 ="Rahul";     //invalid
name1 = "Rahul";     // valid

What is Variable Declaration in JavaScript?

When we define a variable in our JavaScript code without assigning any value, that is called Variable Declaration in JavaScript.

To declare a variable in JavaScript we can use special keywords such as var and let.

let name;   // variable declaration
var let;    // variable declaration

When we only declare a variable without assigning any value, JavaScript treats that variable as undefined.

What is Variable Initialization in JavaScript?

When we assign an initial value to a variable, that is known as variable Initialization in JavaScript. The variable initialization can be done with or after the variable declaration.


const name = "Rahul";       // initialization with declaration

let age;                 // declaration
age = 20;                // initialization

Keywords in JavaScript

There are 64 words reserved in JavaScript which we can not use for variable names. These 64 reserved words are also known as JavaScript keywords, we will be discussing all of these keywords in the further JavaScript tutorial article, for now, here is the list of all 64 JavaScript keywords.

abstract arguments await boolean
break byte case catch
char class const continue
debugger default delete do
double else enum eval
export extends false final
finally float for function
goto if implements import
in instanceof int interface
let long native new
null package private protected
public return short static
super switch synchronized this
throw throws transient true
try typeof var void
volatile while with yield


  • Variable is a name that is used as a container for the data value.
  • A JavaScript variable can be declared and initialize using either of the three keywords const, let, and var.
  • We need to follow the Naming variables rules while giving a name to the variable.
  • A keyword is a reserved word that has a special functionality and meaning in the JavaScript program.
  • There are 64 keywords present in JavaScript.
  • JavaScript is a loosely typed programming language, so we can choose between putting a semicolon; at the end of every statement.

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