Declaring Variables the Right Way in JavaScript

Using var, let and const in JavaScript, and how each differs in their behavior

Different types of variable declarations in JavaScript ( Photo by author )

Variable declaration is one of the basic concepts you can learn when you start learning a new programming language. JavaScript has three different keywords (var, let, and const) that you can use to declare a variable, and they each have their characteristics and behaviors.

In this article, you will see:

• How to declare variables using each keyword
• The scope of the declared variable using each keyword in different scenarios.
• Can we reassign and redeclare variables for each type of declaration?
• A Brief discussion on variable and function hoisting when we declare variables using the var keyword.
• Which one you should and should not use, based on the different scenarios.

So let’s get started about the details on each one of them.

var

A variable declared using var has function scope which means its scope is throughout the function in which it resides and if the same declared outside any function, has a global scope and is accessible throughout the code.

Function scope example

As shown, the variable declared inside a function can only be accessed inside it

Global Scope example

As shown, a variable not inside any function is accessible anywhere

Note: A variable declared using var can be redeclared, so there is a chance that you may override the variable accidentally, here the types let and const comes into play, we will discuss them in the latter…