手动实现Promise.all()

function Promiseall(promises){
    const iterator=Symbol.iterator
    if(!promises[iterator])return;
    return new Promise((resolve,reject)=>{
        const resolvearr=[];
        const rejectarr=[];
        for(let i of promises){
            if(!(i instanceof Promise)){
                i=Promise.resolve(i)
            }
            i.then(res=>{
                resolvearr.push(res)
            })
            .catch(err=>{
                rejectarr.push(err)
            })
        }
        setTimeout(()=>{
            return rejectarr.length===0?resolve(resolvearr):reject(rejectarr[0])
        })
    })
}
const p1=new Promise(res=>res(1))
const p2=new Promise((res,rej)=>rej(2))
const p3=new Promise((res,rej)=>rej(3))
const p4=‘4‘
const su=x([p1,p2,p3,p4])
su.then(res=>{
    console.log(res)
})
.catch(res=>{
    console.log(res)
})