Sharing how to use ajax and promise together

This article mainly shares with you how to use ajax and promise together. Promise can be used to ensure the execution order of ajax requests that need to be completed. Send the second request after the first request returns correctly. Hope it helps everyone.

/*
  定义一个使用promise的ajax请求,这里依赖jquery
  参数中请求url为必填参数
*/
const ajaxPromise=  param => {
  return new Promise((resovle, reject) => {
    $.ajax({
      "type":param.type || "get",
      "async":param.async || true,
      "url":param.url,
      "data":param.data || "",
      "success": res => {
        resovle(res);
      },
      "error": err => {
        reject(err);
      }
    })
  })
}

/*
   第一个请求
*/
let step1 = () => {
    ajaxPromise({
      "url":"",
    }).then(res => {
        console.log("第一个请求正确返回==>"+res);  
        step2(res);  
    }).catch(err => {
        console.log("第一个请求失败");  
    })
}

/*
   第二个请求
*/
let step2 = (res) => {
    ajaxPromise({
      "type":"get",
      "url":"",
      "data":{"name":res}
    }).then(res => {
        console.log("第二个请求正确返回==>"+res);  
    }).catch(err => {
        console.log("第二个请求失败==>"+err);  
    })
}

step1();

---

Write ajaxpromise object in native js

const ajaxPromise =  param => {
  return new Promise((resovle, reject) => {
    var xhr = new XMLHttpRequest();
    xhr.open(param.type || "get", param.url, true);
    xhr.send(param.data || null);

    xhr.onreadystatechange = () => {
     var DONE = 4; // readyState 4 代表已向服务器发送请求
     var OK = 200; // status 200 代表服务器返回成功
     if(xhr.readyState === DONE){
      if(xhr.status === OK){
        resovle(JSON.parse(xhr.responseText));
      } else{
        reject(JSON.parse(xhr.responseText));
      }
     }
    }
  })
}

---

Some points about using promise:

1. How to use : First create a promise object new Promise(), judge whether the execution is successful or failed based on business requirements, call resovle() if successful, and call reject() if failed.

2. Then(onFulfilled, onRejected) of the Promise object has two parameters. OnFulfilled is executed successfully, and onRejectd is executed if it fails.

   p.then(function(value) {
      // fulfillment成功
     }, function(reason) {
     // rejection失败
   });
   
   //不过通常会使用catch()来捕获失败，上段代码通常写为：
   p.then(function(value) {
       // fulfillment成功
   }).catch(function(reason) {
       //rejection失败
   })

3. Then of the Promise object () will return a new Promise object

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