2Block-Scoped Declarations: let and const
In this chapter you'll learn how the new
let and
const declarations work and what problems they solve. Throughout the chapter, you'll see some behaviors of
var that have proved problematic, and you'll learn how
let and
const solve those problems. You'll see how
let and
const provide true block scope and prevent confusion caused by repeated declarations or by using a variable before you initialize it. You'll discover how block scope means you can use
let to avoid the traditional “closures in loop” problem, and how
const lets you create constants: “variables” whose values cannot change. You'll learn how
let and
const avoid creating even more properties on the already-overburdened global object. In short, you'll learn why
let and
const are the new
var, and why
var no longer has a place in modern JavaScript programming.
AN INTRODUCTION TO LET AND CONST
Like
var,
let declares variables:
let x = 2;x += 40;console.log(x); // 42
You can use
let anywhere you can use
var. Just as with
var, you ...
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