js函数重载

 function createOverload(){
      var callMap=new Map();
      function overload(...args){
        const key=args.map((args)=>typeof args).join(',')//得到形如"string,number"的字符串
        const fn =callMap.get(key)//获取之前注册过的函数
        if(fn){
          return fn.apply(this,args)
        }
        throw new Error('no matching function')
      }
      overload.addImpl=function(...args){
        const fn=args.pop()
        if(typeof fn !=='function'){
          return
        }
        callMap.set(args.join(','),fn)
      }
      return overload
    }
const getUsers=createOverload()
getUsers.addImpl(()=>{
  console.log('======查询所有用户');
})
const searchPage=()=>{(page,size=10)=>{
  console.log('页码和每页数量',page,size)
}}
//当有2个条件需要使用同一个函数,上方的size默认值才显得有意义
getUsers.addImpl('number',searchPage)
getUsers.addImpl('number','number',searchPage)
getUsers.addImpl('string',(name)=>{
  console.log('======传入了一个字符串',name);
})
getUsers.addImpl('string','string',(name,name2)=>{
  console.log('======传入了2个都是字符串',name,name2);
})
getUsers('a','b')