3-学习TypeScript（断言）

类型断言有两种形式

let val:string ='abcdef'
写法一:<尖括号>语法
let val1:any = (<string>val).length
写法二：as语法
let val2:any =(val as string).length

用法

window.a =1 //类型“Window & typeof globalThis”上不存在属性“a”
(window as any).a =1

let number = (user:number|string):void=>{
  console.log(user.length)//类型“string | number”上不存在属性“length”
}
number('33')

let number = (user:number|string):void=>{
  console.log((user as string).length)
}
number('33')