ts-类型别名、类型断言

// 类型别名

type PlusType = (x:number,y:number)=>number

function sum(x:number,y:number):number{
  return x+y
}

const sum2:PlusType = sum

type NameResolver = ()=>string
type NameOrResolver = string | NameResolver
function getName(n:NameOrResolver):string{
  if(typeof n==="string"){
    return n;
  }else{
    return n()
  }
}

// 类型断言
function getLength(input:string|number):number{
  // const str = input as String;
  // if(str.length){
  //   return str.length
  // }else{
  //   const number = input as number;
  //   return number.toString().length
  // }

  if((<string>input).length){
    return (<string>input).length
  }else{
    return input.toString().length
  }
}