types

Boolean

Number

String

Array

Tuple 元组类型

Enum

Any

Void

Null and Undefined

Never

Type assertions 类型申明

A note about  let

You may’ve noticed that so far, we’ve been using theletkeyword instead of JavaScript’svarkeyword which you might be more familiar with. Theletkeyword is actually a newer JavaScript construct that TypeScript makes available. We’ll discuss the details later, but many common problems in JavaScript are alleviated by usinglet, so you should use it instead ofvarwhenever possible.