let Vs var Vs const in Javascript
JavaScript is a versatile and widely used programming language that offers multiple ways to declare variables, including let, var, and const. Each of these declarations serves a specific purpose and has its own scope and behavior. In this blog post, we’ll dive into the differences between let, var, and const in JavaScript with examples to help you understand when and how to use them effectively.
This post was originally posted at https://agrawalsuneet.github.io/blogs/let-vs-var-const-in-javascript/ and later reposted on Medium.
var — The Traditional Variable Declaration
var is the oldest way to declare variables in JavaScript. Variables declared with var are function-scoped, which means their scope is limited to the function they are declared in or the global scope if declared outside any function.
Example:
function exampleVar() {
var x = 10;
if (true) {
var x = 20; // This reassigns the outer 'x'
}
console.log(x); // Outputs 20
}In the above example, the if block doesn’t create a new scope for x, so it reassigns the outer x to 20.
let — Block-Scoped Variables
let was introduced in ECMAScript 6 (ES6) to address some of the issues with var. Variables declared with let are block-scoped, meaning they are confined to the block (enclosed by curly braces) in which they are defined.
Example:
function exampleLet() {
let x = 10;
if (true) {
let x = 20; // This is a separate 'x' from the outer one
}
console.log(x); // Outputs 10
}Here, the inner x is distinct from the outer x, thanks to let’s block-level scope.
const — Constants
const is another ES6 addition that allows you to declare variables that cannot be reassigned after their initial value is set. Like let, const is block-scoped.
