ECMAScript 2015 or commonly called as ES6 specification of JavaScript introduced let and const

let

let is the new var. let could be used to declare variables, just like var.

Differences between let and var are

  • let variables are block scoped.
  • Global let variables are not properties on the global object.
  • Loops of the form for (let x...) create a fresh binding for x in each iteration.
  • It’s an to try to use a let variable before its declaration is reached.
  • Redeclaring a variable with let is a SyntaxError.
const

Variables declared with const are like let except you can’t assign to them, except at the point where they are declared. The const declaration creates a read-only reference to a value. It does not mean the value it holds is immutable, just that the variable identifier cannot be reassigned.

References