Understanding the Key Differences Between var, let, and const in JavaScript

JavaScript offers three ways to declare variables: var, let, and const. While they all serve the same purpose—storing values—their behavior, scope, and usage differ significantly. Understanding these distinctions is crucial for writing clean, bug-free, and modern JavaScript code.

Not a Medium member? Read this article here

A Brief History of Variable Declarations in JavaScript

In the early days of JavaScript, the var keyword was the only way to declare variables. However, var came with some quirks, such as unexpected behavior in scoping and hoisting. To address these issues and enhance variable management, ES6 (ECMAScript 2015) introduced let and const. These additions brought better scoping rules and the ability to declare constants, making JavaScript more predictable and reliable.

Key Differences Between var, let, and const

1. Scope

• var: Function-scoped
  Variables declared with var are limited to the function in which they are defined. They ignore block-level scope, leading to potential issues.

if (true) {
    var x = 10;
}
console.log(x); // Output: 10