手写promise.all

function PromiseAll(promiseArray){
  retrun new Promise((resolve,reject)=>{
      if(!Array.isArray(promiseArray)){
        return reject(new Error('传入的参数必须是数组'))
    }
    const res = [];
      for(let i = 0;i<promiseNums;i++){
        const isPromise = Object.prototype.toString.call(promiseArray[i]==='[object Promise]')
        if(isPromise){
          promiseArray[i].then(result=>{
            res.push(result);
        })
      }else{
          res.push(promiseArray[i]);
      }
    }
  })
}
//不需要判断
function PromiseAll(promiseArray){
  retrun new Promise((resolve,reject)=>{
      if(!Array.isArray(promiseArray)){
        return reject(new Error('传入的参数必须是数组'))
    }
    const res = [];
    const promiseNums = primiseArray.length;
      for(let i = 0;i<promiseNums;i++){
        Promiser.resolve(promoiseArray[i]).then(value=>{
          res.push(value);
        if(res.length===promiseNums){
            resolve(res);
        }
      })
    }
  })
}
//需要顺序保持一致
function PromiseAll(promiseArray){
  retrun new Promise((resolve,reject)=>{
      if(!Array.isArray(promiseArray)){
        return reject(new Error('传入的参数必须是数组'))
    }
    const res = [];
    const promiseNums = primiseArray.length;
    let counter = 0;
      for(let i = 0;i<promiseNums;i++){
        Promise.resolve(promoiseArray[i]).then(value=>{
          counter++;
        res[i] = value;
        // 不能通过.length判断
        if(counter === promiseNums){
            reolve(res);
        }
      }).catch(e=>rejct(e))
    }
  })
}

Promise缓存

const cacheMap = new Map();
//装饰器模式
function enableCache(target,name,descriptor){
    const val = descriptor.value;
  descriptor.value = async function(..args){
      const cacheKey = name + JSON.stringify(args);
    if(!cacheMap.get(cacheKey)){
        const cacheValue = Promise.resolve(val.apply(this,args)).catch(_=>{
          cacheMap.set(cacheKey.null);
      })
      cacheMap.set(cacheKey,cacheValue);
    }
    return cacheMap.get(cacheKey);
  }
  return descriptor
}
@enableCache

• 考虑时效