ts基础-3.联合类型与类型断言

联合类型

function getNum(num:string|number):number{
    return 1
}


getNum(123)
getNum("354")

let div:HTMLElement|null = document.getElementById("#div")

function clearTimeout(id: number | undefined): void;

类型断言

就是认为将某一种不确定的类型断言为确定的类型

只是在编辑器层面进行的欺骗行为

let img = document.getElementById("#img")

// 报错
img.src = "http://xxx.xxx/img"

let img = document.getElementById("#img") as HTMLImageElement
img.src = "http://xxx.xxx/img"

let img = <HTMLImageElement>document.getElementById("#img")
img.src = "http://xxx.xxx/img"

两种写法

value as Type
<Type>value

function getAny():any{
    return ""
}

let s = (getAny()as string).charAt()
let s = (<string>getAny()).charAt()