联合类型&交叉类型

1、联合类型 表示取值可以为多种类型中的一种。

let a:number|string
a = 1
a = "hello"

//或
function fn(arg:string | number){
    console.log(arg)
}

fn("hello")
fn(1)

//练习

let a:number | string = "1"

let arr:Array<number|string>=[1,"1"] //数组

function fn(arg:Array<number>|number){ //函数
  
}

2、交叉类型 表示取值为多种类型的全部情况

interface a{
    name:string
    age:number
}

interface b{
    sex:string
    age:number
}

let obj:a&b = {name:"小明",age:18,sex:"男"}

//练习

interface Person {
  name: string;
}

interface Student {
  age: number;
}

let a: Person & Student = {
  name: '张三',
  age: 18
};

3、类型别名

• 类型别名就是自定义类型

type x = number | string

let a:x = 1//ok
let b:x = "1"//ok
let c:x = true//error

//练习
type Person = {
  name: string;
  age: number;
};

let p: Person = {
  name: '张三',
  age: 18
};

案例

• 用type来定义数组

//表示数组的值即可以是字符串也可以是数字
type Arr = (string|number)[]

let arr:Arr = [1,"2",3]

• 用type来定义对象

type Obj = {name:string,age?:number,readonly sex?:string}

let obj:Obj = {name:"小明",sex:"男"}

obj.sex = "女"//报错，不能修改

• 用type来定义函数

type Fn = (arg:number)=>number

let fn:Fn = function(arg:number):number{
    return arg
}

console.log(fn(1))