TLDR:

const Not reassignable, block scope

let Reassignable, block scope

var Reassignable, function scope

Tabulated data

Type Scope Reassignable Mutable Hoisted Temporal dead zone
const Block No Yes * Yes Yes
let Block Yes Yes Yes Yes
var Function Yes Yes Yes No

Note: const are mutable in that arrays and objects can be mutated, since this is not a reassignment.

Hoisting

In JS, variable declarations are ‘hoisted’ to the top of their scope on execution. This means that in written code, one can reference a variable (in relevant scope) that has not yet been declared.

Applies to all, var, let and const.

But, referencing let and const before assignment will cause a reference error, so in practice it does not feel like typical var hoisting.

console.log(myVar); // ok
var myVar = 2;

console.log(myVar); // raises a ReferenceError !
let myVar = 2;

This is called

Temporal dead zone

When a reference error appears due to referencing a let or const before assignment, even though the declaration has in fact been hoisted.