JavaScript Tutorial – Variables

In this tutorial, you will learn about JavaScript variables and how to declare, initialize and use variables in JavaScript applications.

What Are JavaScript Variables?

A variable is storage for data value and the date value can be changed later on.

How to Declare JavaScript Variables

Variables can be declare using any of the 3 reserved keywords, var, let and const. There are 3 rules for JavaScript variable naming convention:

• Variable names must start with a letter, underscore, or dollar sign.
• A variable name cannot be the same as the reserved keywords.
• Variable names are case-sensitive. For example, Hello and hello are two different variables.

var x;
let y;
const z;

If you plan to use a long name for your variables, make sure they follow camelCase.

let name;
let myName;
let ourFirstName;

How to Initialize JavaScript Variables

All the variables we declared so far are undefined. This is because we didn’t initialize their values yet. To initialize a variable, you just need to add an equal sign (=) to the right of the variable name and assign a value.

For example, the following example declares a variable called name and initializes it to “Jay”:

let name;
name = "Jay";

Can you also declare and initialize the variable on the same line:

let name = "Jay";

How to Change Value of a Variable

Once you initialize a variable, you can change its value by assigning a different value. For example:

let name = "Jay";
name = "Jack";
document.write(name);

What is Constant Variable in JavaScript

A constant variable is a variable that holds a value that does not change. You can use the keyword const to declare a constant variable. Once a constant is defined, you cannot change its value.

const site = "WhatAboutHTML";