利用js实现Ajax并发请求限制请求数量的示例代码

var p = function () {
 return new Promise(function (resolve, reject) {
  setTimeout(() => {
   console.log('1000')
   resolve()
  }, 1000)
 })
}
var p1 = function () {
 return new Promise(function (resolve, reject) {
  setTimeout(() => {
   console.log('2000')
   resolve()
  }, 2000)
 })
}
var p2 = function () {
 return new Promise(function (resolve, reject) {
  setTimeout(() => {
   console.log('3000')
   resolve()
  }, 3000)
 })
}


p().then(() => {
 return p1()
}).then(() => {
 return p2()
}).then(() => {
 console.log('end')
})

var promises = function () {
 return [1000, 2000, 3000].map(current => {
  return new Promise(function (resolve, reject) {
   setTimeout(() => {
    console.log(current)
   }, current)
  })
 })
}

Promise.all(promises()).then(() => {
 console.log('end')
})

Promise.all(promises: []).then(fun: function);

function multiRequest(urls = [], maxNum) {
 // 请求总数量
 const len = urls.length;
 // 根据请求数量创建一个数组来保存请求的结果
 const result = new Array(len).fill(false);
 // 当前完成的数量
 let count = 0;

 return new Promise((resolve, reject) => {
  // 请求maxNum个
  while (count < maxNum) {
   next();
  }
  function next() {
   let current = count  ;
   // 处理边界条件
   if (current >= len) {
    // 请求全部完成就将promise置为成功状态, 然后将result作为promise值返回
    !result.includes(false) && resolve(result);
    return;
   }
   const url = urls[current];
   console.log(`开始 ${current}`, new Date().toLocaleString());
   fetch(url)
    .then((res) => {
     // 保存请求结果
     result[current] = res;
     console.log(`完成 ${current}`, new Date().toLocaleString());
     // 请求没有全部完成, 就递归
     if (current < len) {
      next();
     }
    })
    .catch((err) => {
     console.log(`结束 ${current}`, new Date().toLocaleString());
     result[current] = err;
     // 请求没有全部完成, 就递归
     if (current < len) {
      next();
     }
    });
  }
 });
}

  // 任务列表->新建任务
 
  uploadFile() {
   let _this = this;
   var uploadThreadLimitNums = 3,
    uploadThreadNums = 0,
    sendFinishNum = 0,
    resultFinishNum = 0;
   var marks = 0;
   var tasks = [];
   var upload = function () {
    while (uploadThreadNums < uploadThreadLimitNums) {
     if (sendFinishNum >= _this.fileList.length) {
      if (resultFinishNum >= _this.fileList.length) {
       creatTask(); // 完成请求
      }
      return;
     }
     (function (j) {
      let item = _this.fileList[j];
      let p = new FormData();
      p.append("file", item);
      tasks.push(
       axios({
        method: "post",
        url: `${window.UL_CONFIG.BASEURL}/api/files/upload`,
        data: p,
        onUploadProgress: (progressEvent) => {
         for (let i in _this.rowData) {
          _this.rowData[i].name === item.name
           ? (_this.rowData[i].percent = Math.round(
             (progressEvent.loaded / progressEvent.total) * 100
            ))
           : "";
         }
        },
       })
        .then((res) => {
        /* let obj = {};
         obj.url = `${window.UL_CONFIG.BASEURL}/api/files/${res.data}`;
         obj.fileName = item.name;
         obj.fmt = _this.ruleForm.format;
         obj.samplingRate = _this.ruleForm.samplingRate;
         fileUrls.push(obj); */
        })
        .catch((e) => {
           ? (_this.rowData[i].percent = 0)
         _this.$notify.error({
          title: "错误",
          message: "服务连接错误 "   item.name   " 未上传成功",
         });
        .finally(() => {
         uploadThreadNums--;
         resultFinishNum  ;
         upload();
      );
     })(sendFinishNum);
     uploadThreadNums  ;
     sendFinishNum  ;
    }
   };
   var creatTask = function () {
    axios.all(tasks).then((res) => {
     // 新建上传任务
      /* let fd1, fd2, calcFlag, flagArr, language;
     fd1 = {};
     flagArr = Object.assign([], _this.ruleForm.checkList);
     if (_this.ruleForm.recognize == "自动识别") {
      flagArr.push("2");
     calcFlag = flagArr.reduce(
      (accu, curr) => Number(accu)   Number(curr)
     );
     _this.ruleForm.recognize == "自动识别"
      ? (language = "")
      : (language = _this.ruleForm.recognize);
     fd1.processContent = calcFlag;
     fd1.remark = _this.ruleForm.remark;
     fd1.name = _this.ruleForm.taskName;
     fd1.fmt = _this.ruleForm.format;
     fd1.samplingRate = _this.ruleForm.samplingRate;
     fd1.language = language;
     fd1.type = 1; // type: 1 语音, 2 视频
     fd1.files = fileUrls; */
     newTask(fd1).then((res) => {
      /* _this.cmpltBtnState = false;
      _this.$store.commit("setTaskId", res.data.id);
      _this.submitFailNumber = res.data.submitFailNumber; */
      _this.$parent.dataInit();
     });
    });
   upload();
  },