JavaScript works behind the scenes —— hoisting and TDZ(变量提升和暂时性死区)

JavaScript works behind the scenes —— hoisting and TDZ(变量提升和暂时性死区)

concept

Makes some types of variables accessible/usable in the code before they are actually declared. "Variables lifted to the top of their scope"

(让某些类型的变量可以在他们被真正声明之前就可以使用，将他们提升到最高层的作用域)

how to hoisting?

why hoisting

1. using functions before actual declaration
2. var hoisting is just a byproduct

TDZ(Temporal dead zone)(暂时性死区)

变量用let/const声明之前就调用，那时不可用，在声明之前的scope成为暂时性死区。

example：

console.log(`Hello ${name}`)
let name = 'kihyun'

throw error: Reference Error: Cannot access 'name' before initialization

why TDZ?

1. make it easier to avoid and catch errors: accessing variables before declaration is bad practise and should be avoided
2. make const varibles actually work