Var, Let, and Const – What's the Difference?
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In JavaScript, let, var, and const are used to declare variables, and they have different behaviors and scoping rules. Additionally, block scope variables are a concept related to how variables are scoped within code blocks. Let me explain each of these concepts:
var:
var is the oldest way to declare variables in JavaScript.
Variables declared with var are function-scoped, meaning they are only accessible within the function in which they are declared.
Variables declared with var are also hoisted, which means that they are moved to the top of their containing function or script before the code is executed. This can sometimes lead to unexpected behavior.
let:
let was introduced in ES6 (ECMAScript 2015) to address some of the issues with var.
Variables declared with let are block-scoped, which means they are only accessible within the block in which they are defined, such as inside a loop, conditional statement, or a function.
Variables declared with let are not hoisted, so they are only accessible after the declaration statement in the code.
const:
const is also introduced in ES6 and is used for declaring constants.
Variables declared with const are block-scoped like let.
The key difference is that variables declared with const cannot be reassigned after their initial value is assigned. They are read-only.
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