Web Components in Action

A.2. Rethinking variables with ES2015

Strictly speaking, you’re free to keep using var whenever you want. Declaring variables this way has worked for as long as JS has been in existence, and it’s not changing anytime soon.

A.2.1. Variable declaration with let

ES2015 brings us two more ways to declare your variables: let and const. In terms of usage, not much has changed—things are just a bit stricter and a little saner. With let, you may declare your variables, just as you always have with var:

var x = 5; // old way
let x = 5; // new way

The difference between let and var is a matter of scope. Variable declarations made with let are a bit more familiar to users of other programming languages. The variables will exist only in the block they ...