如何处理承诺的失败Ajax请求

Question

I am making multiple ajax requests like this

 imgPromises = []; imgPromise1 = $.ajax({ url: s3Url, type: "POST", data: s3FormData, mimeType: "multipart/form-data", contentType: false, cache: false, processData: false }).done(function(data, status, formXHR) { x = formXHR['responseText'].toString(); var uploadedUrl = x.match("<Location>(.*)</Location>")[1]; if ($(this).attr('id').startsWith('inp')) { if ($(this).attr('id').startsWith('inp')) $('footer').css('background-image', 'url(' + uploadedUrl + ')'); footerBackground = $('footer').css('background'); } }).fail(function() { console.log("in ajax fail"); }.bind(this)); imgPromises.push(imgPromise1); imgPromise2 = $.ajax({ url: s3Url, type: "POST", data: s3FormData, mimeType: "multipart/form-data", contentType: false, cache: false, processData: false }).done(function(data, status, formXHR) { x = formXHR['responseText'].toString(); var uploadedUrl = x.match("<Location>(.*)</Location>")[1]; if ($(this).attr('id').startsWith('inp')) { if ($(this).attr('id').startsWith('inp')) $('footer').css('background-image', 'url(' + uploadedUrl + ')'); footerBackground = $('footer').css('background'); } }).fail(function() { console.log("in ajax fail"); }.bind(this)); imgPromises.push(imgPromise2); Promise.all(imgPromises.then(function() {}); 

If any of the promise( imgPromise1 or imgPromise2 ) fails then it didn't go to Promise.all .

I want that in every case it should go to Promise.all .

Answer 1

you are using then in the wrong place.

const Fail = function(error){this.error=error;};//special Fail type value
const isFail = o=>(o&&o.constructor)===Fail;//see if item passed is fail type
const isNotFail = o => !isFail(o);//see if item passed is not fail type
Promise.all(imgPromises
  .map(
    p=>Promise.resolve(p)/**convert to real promise*/
  ).map(
    p=>p.catch(error=>new Fail(error))//single request failed, resolve with Fail value
  )
)
.then(function (responses) {
  // successes = responses.filter(isNotFail)
  // failed = responses.filter(isFail)
})
.catch(function (err) {
  //handle error
});

MDN page for Promise.all

Answer 2

Depending on the version of jQuery you are using you can use .catch and return something in catch that the promise will resolve with.

jQuery's version of Promise.all ($.when) will not reject if any of the deferred (is jQuery promise implementation) rejects.

This is only since version 3 since jQuery's deferred before this version did not behave like standardized promises (the promises native to modern browsers).

 function makeRequest(num){//returning $.Deferred like $.ajax will var d = $.Deferred(); setTimeout(() => { if(num>1){//reject if number passed is higher than 1 d.reject("Rejecting over one"); return; } d.resolve(num) }, 10); return d.promise(); } $.when.apply(//jQueries Promise.all need apply to pass array of "promises" $, [1,2].map(//map numbers 1 and 2 to deferred 1 will resolve 2 rejects function(num){ return makeRequest(num) .catch(//catch rejected deferred function(error){return "error in:"+num; }//resolve with this ); } ) ).then(//both deferred (=jQuery promise like) are resolved function(){ console.log("it is done",[].slice.apply(arguments)); } ) 

 <script src="https://code.jquery.com/jquery-3.3.1.min.js" integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script> 

However, you try the same with version 2 of jQuery and it won't work because implementation of deferred/promise is not like standard promises in versions lower than 3. You could convert Deferred to real promise but if you want to support older browsers you need Promise polyfil :

 console.log("jQuery version",jQuery.fn.jquery); function makeRequest(num){//function returning jQuery deferred (could be $.ajax) var d = $.Deferred(); if(num>1){ //now this will throw an error throw("Rejecting over one"); } setTimeout(() => { d.resolve(num) }, 10); return d.promise(); } Promise.all( [1,2].map( function(num){ //convert deferred to real Promise (having catch) if makeRequest throws then promise is rejected return Promise.resolve().then(()=>makeRequest(num)) .catch( function(error){return "error in:"+num; }//resolve to error in... string ); } ) ).then( function(){ console.log("it is done",[].slice.apply(arguments)); } ) 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 

Answer 3

To wait until all promises finish their tasks (resolve and/or reject) we return value of catch() for each promise.

In this case we use .then() to receive all information.

We can filter both rejected and resolved data using filterInformation helper function.

Example:

 const mockResolvePromise = (message) => { return new Promise((resolve) => { resolve(message) }) } const mockRejectPromise = (messageError) => { return new Promise((_, reject) => { reject(messageError) }) } const ajax0 = mockResolvePromise({ nice: 'data' }) const ajax1 = mockRejectPromise('bad error'); const ajax2 = mockRejectPromise('semi bad error'); const ajax3 = mockRejectPromise('super bad error'); const ajax4 = mockResolvePromise({ hello: 'handsome' }) const promises = [ajax0, ajax1, ajax2, ajax3, ajax4]; // Now lets add catch const promisesWithCatch = promises.map(p => p.catch(e => { return { error: e } })) const filterInformation = (stuff) => { return stuff.reduce((prev, current) => { if (current.error) return { ...prev, errors: [...prev.errors, current.error] }; return { ...prev, data: [...prev.data, current] } }, { errors: [], data: [] }) } Promise.all(promisesWithCatch) .then(filterInformation) .then(data => console.log(data)) 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>