Everything you need to know about Javascript Variables

Hey guys in this post, we will discuss Javascript variables with Examples

What are variables?

A variable is a named storage for data. Each variable must have a unique name which is called identifier. Variables can be hard-coded to hold predefined values or dynamically generated.

Declaring variables

You can easily declare a variable using the let keyword followed by the name of the variable

let email;
email = "[email protected]";

You have the option to declare a variable and assign a value later or do both at once

let email = "[email protected]";
let loggedIn = false;

Changing value

You can easily change the value of a variable by easily assigning a new one

let testVariable = "hello";
testVariable = "world";

Javascript is dynamically types do you can even assign a value of a different type (although that is not advised)

let testVariable = "hello";
testVariable = 10;
testVariable = false;

Naming rules

Javscript variable names can only contain letters, numbers or the symbols $ and _

However, the first character cant be a number and you cant use reserved keywords (such as let or return) for variable names.

//valid variable names
let test1;
let variable_name;
let user_1;

//invalid varaible names
let 1test;
let varaible-test;
let return;


If the value of your variable is constant and won’t be re-assigned you can use const instead of let.

const welcomeMessage = "hello world";

These are useful to create a distinction between constant and changeable variables

const email = "[email protected]";
let isLoggedIn = true;

Uppercase constants

It has also become common practice to use constant aliases for known values that are used throughout a site or application. These are written with uppercase letter and underscores.

const PRIMARY_BRAND_COLOR = "#1c3aa4";
const CONTACT_EMAIL = "[email protected]";
const COMPANY_REG_NUMBER = "0123456789";

There is technically no difference between them as for as javascript is concerned, it is just a style choice to differentiate them.

What about var?

You can still declare variables using var, however the practice is now considered outdated.

//old standard
var message = "hello world";

//new standard
let message = "hello world";

variable declared with var aren’t scoped and have various other flaws, so unless you need to support a really old browser its best to use let and const variables.


  • Use let to declare variables with changeable values
  • Use const to declare constant, non changeable values
  • Follow the naming rules and name your variables well
  • Use uppercase constants for hard-coded global constant values
  • Don’t use var to declare variables unless you require legacy browser support

Bushan Sirgur

Hey guys, I am Bushan Sirgur from Banglore, India. Currently, I am working as an Associate project in an IT company.

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