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I use in my application a request REST API which works asynchronous. How I can do to know the request is done?

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    You can set alert or flag kind of logic for that. You can stop async behavior of REST using async:false, Sep 5, 2016 at 2:34
  • Theres success and fail method. Also if you want to do something after a call is complete, call that method from success or Complete method of Ajax call.
    – Taran Goel
    Sep 5, 2016 at 7:49
  • If an answer was helpful could you remove your question from the SO unanswered list, by marking it as answered, tnx Jun 4, 2017 at 8:20

2 Answers 2

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Ajax/REST calls do let know when they succeed or fail, that is the whole point.
And you do not need to convert code to synchronous calls.

In the old days you would use Callback functions, nowadays you use Promises
(you can even mix these, Callbacks are executed first)

The best post explaining all this async stuff is:
(it has 2757 upvotes, you can +1)

https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call

Code

because Link-only posts are not encouraged and the admins are watching me

orginally from a jQuery answer

Here is code with both Callback functions and Methods chained to the $.ajax Promise
learn to use Chrome Snippets to run SP code without going through a long & complex built proces

    console.clear();
    var site=_spPageContextInfo.webAbsoluteUrl;
    var listName='Documents';
    $.ajax({
        url: site + "/_api/web/lists/getbytitle('" + listName + "')",
        method: "GET",
        contentType: "application/json;odata=verbose",
        async: true, // is the default value, so you can leave it out
        headers: {
            "Accept": "application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val()
        },
        success:function(data){//this is a Callback function
            console.log('success Callback', data)
        },
        error:function(data){//this is a Callback function
            console.log('error Callback', data)
        }
    }).done(function(data){//this is a method on the Promise chain
        console.log('success ',data);
    }).fail(function(data){//this is a method on the Promise chain
        console.error('error ',data);
    }).always(function(data){//this is a method on the Promise chain
        console.log('always ',data);
    });

So the .done method is interchangable with the success Callback

Note that they are both executed in this example.. Callbacks first.

(modern) Promises are more powerful, (oldschool) Callbacks are used in most blogposts.

I had to RTFM as well

.success and .error methods you see in blogposts are deprecated since jQuery 1.8 (use .done and .fail) but do still work

Yes you can do ajax without jQuery

You do not need that 90KB library, it is just a fancy wrapper around native JavaScript code:

var site=_spPageContextInfo.webAbsoluteUrl,
    listName='Documents',
    xhr = new XMLHttpRequest(); 
xhr.open("GET",site+"/_api/web/lists/getbytitle('"+listName+"')", true);
xhr.setRequestHeader("Accept","application/json;odata=nometadata");
xhr.setRequestHeader("X-RequestDigest",document.getElementById('__REQUESTDIGEST').value);
xhr.onreadystatechange = function (data) {
  if (xhr.readyState != 4) return;//no response received yet 
  if (xhr.status===200) console.info('success');
  console.info('I got:',listName,data);
};
xhr.send();

A modern replacement for XMLHttpRequest is fetch, but it does have some drawbacks: https://davidwalsh.name/fetch
You do need a polyfill becuase only Microsoft Edge 14 now supports it.

Promises are native JavaScript as well but also require a polyfill, Edge is fine but IE still stinks.
Note that jQuery does done and fail, native JS is then and catch

When diving deeper into REST, be sure to understand the different odata responses: https://blogs.office.com/2014/08/13/json-light-support-rest-sharepoint-api-released/

Microsoft is pushing an open-source team to write a wrapper around SP-REST functionality. https://github.com/OfficeDev/PnP-JS-Core
(Remember: this does require Promise & Fetch polyfills to run)

Stackoverflow related posts:

iJS iREST

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    This answers only the case when you use JavaScript... Sep 5, 2016 at 8:05
  • Correct. But you have not been around for nearly 2 years, Wictor (i.imgur.com/TOr2bHk.jpg) If someone asks a REST question here on SO, and they tag it 'online' I will go all-in with my SO-points it is a JavaScript question. (btw. +1 for spelling JavaScript correct 😉 Sep 5, 2016 at 8:14
  • LOL. Nuff said. Sep 5, 2016 at 8:19
  • It wouldn't be a bad idea, some more gamification/poker with SO credits. Current system sucks. Sep 5, 2016 at 8:34
  • Love that you saved old pictures of my SO points! Sep 5, 2016 at 8:35
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There's no acknowledgement of asynchronous requests, it's kind of the point. If you want to know if the request succeeds or fails you either have to change your code to synchronous operations OR use asynchronous methods in your code to wait for the response (exactly how, depends on where your code is executing; JavaScript, C# etc).

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