28.用Promise.all实现限制三个并发的网路请求

const limit = 3;
let count = 100;
// 网络请求
const images = Array.from({ length: 100 }, (_, i) => `Image ${i + 1}`);
const axios = function (url) {
  return new Promise(function (resolve, reject) {
    const randomNum =  Math.floor(1000 * Math.random());
    setTimeout(() => {
      resolve(url + ` randomNum: ${randomNum}`);
    }, randomNum);
  });
};
// 结果列表
let resList = [];
// 当前并发数
let currRequestTimes = 0;
// 递归函数，按顺序上传图片
function uploadImagesInOrder() {
    return new Promise(function (resolve, reject) {
        if(images.length > 0){
            const url = images.shift();
            axios(url).then((res) => {
                resList.push(res);
                console.error('res', res);
                if(images.length > 0){
                    uploadImagesInOrder();
                }else{
                    resolve()
                }
            });
        }else{
            resolve();
        }
    })
}

let promiseList = [];
async function startUpload(){
  // 并发
  for (let i = 0; i < limit; i++) {
    promiseList.push(uploadImagesInOrder());
  }
  const res =  await Promise.all(promiseList);
  console.log('end');
}
startUpload();