Скачать или смотреть JavaScript | Difference between var, let and const

In JavaScript, var, let, and const are used to declare variables, but they have some differences in terms of scope and mutability.

var was the traditional way to declare variables in JavaScript before the introduction of let and const. Variables declared with var are function-scoped, meaning they are accessible throughout the entire function in which they are defined. If var is used outside of any function, the variable becomes globally scoped, and accessible throughout the entire program. Additionally, variables declared with var are hoisted to the top of their scope, which means they are moved to the top during the compilation phase.

let was introduced in (ES6) and provides block scoping. Variables declared with let are limited in scope to the block (enclosed by curly braces) in which they are defined, including loops, if statements, and functions. Unlike var, variables declared with let are not hoisted, so they must be declared before they are used.

const also came with ES6 and is used to declare variables that are constants and cannot be reassigned once they are defined. Like let, const is block-scoped and not hoisted. It provides immutability to the assigned value, but it doesn't make the variable itself immutable. This means you can't reassign a new value to a const variable, but the properties of objects declared with const can be modified.


It's generally recommended to use let and const over var because they provide more predictable scoping behavior and help avoid certain issues that can arise from the hoisting and function-level scope of var. The choice between let and const depends on whether you need to reassign the variable or ensure its immutability.