ts 基本数据类型

let name: string = "whbbit" // name 的值只能是字符串类型
let age: number = 25 // age的值只能是数值类型
let work: boolean = false // work的值只能是true/false

let stringArr: string[] // 数组里的值只能是字符串

let obj1: object // obj1必须是一个对象
let obj: { name: string; age: number } // obj这个对象中只能包含name和age属性，且类型必须是规定的类型

let obj1: { name: string; age: number; work: boolean } = {
  name: "whbbit",
  aage: 25,
}
console.log(obj1) // 编译时会有报错，Property 'work' is missing in type '{ name: string; age: number; }' but required in type '{ name: string; age: number; work: boolean; }'.

let obj: { name: string; age: number; work?: boolean } = {
  name: "whbbit",
  age: 25,
}
console.log(obj)

let name = "whbbit" // 等同于 -> let name: string = 'whbbit'

let a: string | number // 表示a可以是字符串也可以是一个数值
a = "whbbit"
a = 20

let b: string | number | boolean
b = "whbbit"
b = 20
b = false

let arr: (string | number)[] = [] // 数组内容只能为字符串或数值类型
let arr1: Array<string | number> = [] // 使用泛型

let a: any
a = "whbbit"
a = 10
a = false
a = ["whbbit"]

let arr: Array[any]
let arr1: any[]

class Animal {
  constructor() {}
  get = () => "whbbit.cn"
}

const cat: any = new Animal()

let a: any
let a1: string = a // 不会进行报错，ts不做类型校验

let b: unknown
let c: string = b // ts校验报错，类型不匹配

let b: unknown
let c: string = b as string // 断言变量b一定是一个string类型的值

let a: string = "20"
let b: number = a as number // 会报错，不能对已经声明类型的值进行断言

let a: string = "20"
let b: number = a as unknown as number

let a: void = null
a = undefined

function err(): never {
  throw new Error("err")
}

function printString(content: any): void {
  console.log(content)
}

function throwError(err): never {
  throw new Error(err)
}

let a: null = null
let b: undefined = undefined

let a: string
a = null
a = undefined
// 这时不会报错