Detailed explanation of several ajax request methods that may be encountered in actual combat-JS Tutorial-php.cn

This article mainly shares with you several ajax request methods that may be encountered in actual combat. The article introduces the ajax sample code in very detail, which has certain reference value for everyone. Friends who are interested in ajax follow Let’s take a look together.

Preface

Recently I am working on a functional page for measuring the speed of a single node. The logic of the speed measurement is that when measuring the upload speed, the front end transmits 5m Send the data to the server, record the time of uploading and returning the data. When measuring the download speed, download 1m of data from the server, record the download and the time of successful download. Ajax synchronization is used for upload and download to avoid the problem of client bandwidth blocking, and Do this 3 times and take the average. During the development process, many detours were made due to the synchronization and asynchronous issues of Ajax, so I also compiled and summarized the business logic I encountered before.

The ajax request method is as follows

1. Ordinary ajax, async means synchronous and asynchronous processing, after success, data will be returned Value, status request status, xhr encapsulates the request header, but it should be noted that not all request header information can be obtained, such as center-length cannot be obtained

$.ajax({ type: "GET", async: true, //异步执行 默认是true异步 url: url, dataType: "json", // jsonp: "callback", success: function(data, status, xhr){ console.log(data);//返回值 console.log(status);//状态 console.log(xhr);//obj console.log(xhr.getResponseHeader("Content-Type"));//application/octet-stream console.log(xhr.getResponseHeader("Center-Length"));//null } });

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2. Sometimes the business logic encountered is like this. Request 2 depends on the return result of request 1, and request 3 depends on the return result of request 2. If it is written in a callback method, it will be very complicated. It's lengthy. There are two solutions. First, let's look at the ES5 solution

(1) The ES5 solution is to use ajax to synchronize. The default ajax is asynchronous, that is, multiple requests are executed at the same time. , after changing to synchronization, ajax is executed one by one, so that ajax2 can get the return result of ajax1

let res1 = "" let res2 = "" $.ajax({ type: 'get', async: false, //同步执行 默认是true异步 url: pars.domain + "/api.php?Action=xxx&date=2017-03-08&t=" + (new Date).getTime(), dataType: 'json', success: function(res) { if(res.code == 0){ res1 = res.data.bandwidth[0] }else{ } } }); $.ajax({ type: 'get', async: false, //同步执行 默认是true异步 url: pars.domain + "/api.php?Action=xxx&date=2017-03-08&dom1111" + res1 + "&t=" + (new Date).getTime(), dataType: 'json', success: function(res) { if(res.code == 0){ res2 = res.data.bandwidth[0] }else{ } } });

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(2) ES6 solution, use The then method of promise has the same effect as above. Ajax will be executed in order, and the subsequent ajax will get the return value of the previous ajax. When written like this, the code will look very smooth

let pro = new Promise(function(resolve,reject){ let url = pars.domain + "/api.php?Action=xxx=2017-03-08&t=" + (new Date).getTime() let ajax = $.get(url, function(res) { if (res.code == 0) { resolve(resData); } else{ } }, "json"); console.log('请求pro成功'); }); //用then处理操作成功，catch处理操作异常 pro.then(requestA) .then(requestB) .then(requestC) .catch(requestError); function requestA(res){ console.log('上一步的结果：'+res); console.log('请求A成功'); let proA = new Promise(function(resolve,reject){ let url = pars.domain + "/api.php?Action=xxx&date=2017-03-08&t=" + (new Date).getTime() let ajax = $.get(url, function(res) { if (res.code == 0) { resolve(resData); } else{ } }, "json"); }); return proA } function requestB(res){ console.log('上一步的结果：'+res); console.log('请求B成功'); let proB = new Promise(function(resolve,reject){ let url = pars.domain + "/api.php?Action=xxx&date=2017-03-08&t=" + (new Date).getTime() let ajax = $.get(url, function(res) { if (res.code == 0) { resolve(resData); } else{ } }, "json"); }); return proB } function requestC(res){ console.log('上一步的结果：'+res); console.log('请求C成功'); let proC = new Promise(function(resolve,reject){ let url = pars.domain + "/api.php?Action=xxx&date=2017-03-08&t=" + (new Date).getTime() let ajax = $.get(url, function(res) { if (res.code == 0) { resolve(resData); } else{ } }, "json"); }); return proC } function requestError(){ console.log('请求失败'); }

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3. jsonp cross-domain, dynamically add script tags to achieve cross-domain. Note that there is a callback that needs to be negotiated with the server

function switchEngineRoomAjax(api,statusChanged){ var api = api; var statusChanged = statusChanged; var url = api + "?method=setStatus" + "&status=" + statusChanged; $.ajax({ type: "GET", url: url, dataType: "jsonp", jsonp: "callback",// 这里的callback是给后端接收用的，前端通过动态添加script标签，完成回调 success: function(res){ if (res.code == 0) { console.log('更改状态 jsonp获取数据成功！'); } else{ } } }); };

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Fourth, you will also encounter this kind of business logic. There are three asynchronous requests ajax1 ajax2 ajax3. It is not necessarily which one returns the data first. After all requests are successful, a callback function is executed. It should be noted that a separate ajax also needs to be new's promise

ajax1:function(){ var promise = new Promise(function (resolve, reject) { var url = "/api.php?Action=xxx; $.get(url, function(res) { if (res.code == 0) { resolve('queryLog完成！'); } else{ } }, "json"); }); return promise }, ajax2: function(){ var promise = new Promise(function (resolve, reject) { var url = "/api.php?Action=xxx; $.get(url, function(res) { if (res.code == 0) { resolve('queryGroupNodeList完成！'); } else{ } }, "json"); }); return promise }, ajax3: function(){ var promise = new Promise(function (resolve, reject) { var url = "/api.php?Action=xxx; $.get(url, function(res) { if (res.code == 0) { resolve('queryGroupNodeMapList完成！'); } else{ } }, "json"); }); return promise }, initQuery: function(){ var mySelf = this; var promiseList = []; var ajax1Promise = mySelf.ajax1(); var ajax2Promise = mySelf.ajax2(); var ajax3Promise = mySelf.ajax3(); promiseList.push(ajax1Promise,ajax2Promise,ajax3Promise); var p1 = new Promise(function (resolve, reject) { console.log('创建1.2秒延时执行promise'); setTimeout(function () { resolve("1.2秒延时执行promise"); }, 1200); }); promiseList.push(p1) Promise.all(promiseList).then(function (result) { console.log('ajax全部执行完毕：' + JSON.stringify(result)); // ["Hello", "World"] mySelf.assembleTableData(); }); },

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The above is all the content of this article, I hope it will be helpful to everyone's learning!

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