typescript详解

类型断言

const ele = document.querySelector('#canvas') as HTMLCanvasElement

const ele = <HTMLCanvasElement>document.querySelector('#canvas')

In

type Fish = { swim: ()=>void }
type Bird = { fly: ()=>void }
function func(method: fish|Bird){
  if('swim' in Fish){
	Fish.swim() 
}
return Bird.fly()
}

instansof

 function func(x: Date | string){
   if(x instanceof Date){
  	console.log(x.getTime()) 
  }else{
    console.log('string') 
}
}

带属性的函数(函数签名)

type IFunc = {
    count: number,
    (value: number): string
}

const getCount: IFunc = value=>{
    return '111'
}
getCount.count = 1;

泛型

function doSomething<T>(a: T):T{
   //检测T的类型，并返回T类型
}
doSomething('hello')

多种泛型

function doSomething<T extends {length:number},B>(a: T, b: T):T // 公共属性条件约束

function doSomething<T extends string|number,B>(a: T, b: B):B{
    //检测T的类型, B的类型， 返回B的类型
   if(typeof b === 'string'){
    return b+'123' as B;
   }
   if(typeof b === 'number'){
    return b*2 as B;
   }
   return b;
 }

 doSomething('hello', 123)