Differences between let, const and var?

var

• function scope,
• can be redeclared,
• its value can change,
• after hoisting it is undefined until assigned.

let

• block scope,
• its value can change,
• can't be redeclared in the same scope.

const

• block scope,
• can't be assigned a new value.

const user = {
  name: "Tom"
};

user.name = "Anna";

this is fine.

We don't change the reference, only the object's contents.

Rule of thumb:

const → by default
let → when the assignment will change
var → I'd rather not use it