TypeScript学习（2）

const enum Direction{
    Up='UP',
    Down='DOWN',
    Right='RIGHT',
    Left='LEFT',
}

function echo(arg:number){
  return arg
}
const result = echo(123)   // result is number
const result = echo('123') // result is string change arg is string
...

function echo<T>(arg:T):T{        // 使用T作为参数占位
  return arg
}
const result:number = echo(123)
const result:string = echo('123')
const result:boolean = echo(true)

function swap<T,U>(tuple:[T,U]):[U,T]{
   return [tuple[1],tuple[0]]
}
const result2 = swap(['string',123])
result2[1] // number
result2[0] // string

function echoWithArr<T>(arg:T):T{
  console.log(arg.length)
  return arg
}
// 会报错，因为T可能没有length，如果给T加约束
function echoWithArr<T>(arg:T[]):T[]{
  console.log(arg.length)
  return arg
}
// 改造成了传T类型的数组，错误取消，但是如果想判断字符串的length呢，如果是对象中含有length呢，上面的改造就不能实现了，继续改造
interface IWithLength{
  length:number;
}
function echoWithLength<T extends IWithLength>(arg:T):T{
   console.log(arg.length)
   return arg
}
const str = echoWithLength('str')
const obj = echoWithLength({length:12,width:'12'})
const arr = echoWithLength([1,2,3])
// 以上都可以满足，问题解决

class Queue<T>{
  private data = [];
  push(item:T){
    return this.data.push(item)
  }
  pop():T{
    return this.data.shift()
  }
}
const queue = new Queue<number>();
queue.push(1)
const queue2 = new Queue<string>();
queue.push('1')

interface KeyPair<T,U>{
  key:T;
  value:U;
}
let kp1:KeyPair<number,string> = {key:123,value="str"}
let kp2:KeyPair<string,number> = {key:"str",value="123"}

let arr:number[] = [1,2,3]
let arr2:Array<number> = [1,2,3,4]

interface IPlus<T> {  // 描述了一个函数的类型
  {a:T,b:T}: T
}
function plus(a:number,b:number){
  return a+b;
}
function connect(a:string,b:string){
  return a+b;
}
const a:IPus<number> = plus;
const b:IPus<string> = plus;

// 别名 type aliases
function sum(x;number,y:number):number {
return x+y
} 
const sum2:(x;number,y:number)=>number = sum
// sum2 太长，用类型别名
type PlusType = (x;number,y:number)=>number
const sum2:PlusType = sum

// 断言 as 分别判断不同类型的不同处理方式
function sum(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
   }
} 
=>
function sum(input:string | number) :number {
   if((<string>input).length){
     return (<string>input).length
   }else{
      return input.toString().length
   }
} 

jQuery('#f00');

{
  "include":["**/ *]
}