What are the key differences between var, let, and const in JavaScript? When would you use each one?

JavaScript

var vs let vs const

var is function scoped and if you try to use a variable declared with var before the actual declaration, you'll just get undefined.
const and let are blocked scoped and if you try to use variable declared with let or const before the declaration you'll get a ReferenceError.
Finally the difference between let and const is that once you've assigned a value to const, you can't reassign it, but with let, you can.

var vs let vs const

var:
  function scoped
  undefined when accessing a variable before it's declared

let:
  block scoped
  ReferenceError when accessing a variable before it's declared

const:
  block scoped
  ReferenceError when accessing a variable before it's declared
  can't be reassigned

00:00

Table of Contents

var vs let vs const