Callback in ajax request

Question

I have made API and trying use it in my jQuery scripts. But having problems with callbacks. My JavaScript:

function findAll() {
    var users;
    $.ajax({
        url: "/user",
        type: "GET",
        dataType: "json",
        success: function (data) {
            users = data;
        }
    });
    return users;
}

Help me return received data, please. Thanks in advance.

You can write a call back function and replace that with success function. var successCallback = function(result){console.log(result)}; success: successCallback — dharmesh, Sep 09 '16 at 14:37
You need to place all logic that depends on the result of the request in the callback. See the question I marked as duplicate for more information — Rory McCrossan, Sep 09 '16 at 14:41

nikjohn · Answer 1 · 2016-09-09T15:07:54.760

0

This will not work because you are returning users synchronously. The value will be undefined.

What is happening is this: - var users is declared and set to undefined by the Javascript engine

the AJAX callback is registered to be called when the XHR request resolves
var users (now = undefined) is returned
users is assigned the response of the XHR request. But alas! It's too late and undefined has already been returned!!

This should work:

function returnUsers(users) {
    return users;
}

var users = findAll(returnUsers);

function findAll(callback) {
 $.ajax({
    url: "/user",
    type: "GET",
    dataType: "json",
    success: callback
 });

}

edited Sep 09 '16 at 15:07

answered Sep 09 '16 at 14:34

nikjohn

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Yes, thats why I'm asking :) – zzheads Sep 09 '16 at 14:34
Updated the answer – nikjohn Sep 09 '16 at 14:35
This also should not, success function return value, but not findAll – zzheads Sep 09 '16 at 14:37
And value of users is undefined still – zzheads Sep 09 '16 at 14:37
This will not work as you are returning from an anonymous function, not the `findAll()` function, so the data is lost. You need to place all logic which depends on the result of the request *within* the callback – Rory McCrossan Sep 09 '16 at 14:40
`This should work` - that does NOT work. – Jamiec Sep 09 '16 at 14:49
Updated the response with the new solution – nikjohn Sep 09 '16 at 14:49
It's still not going to work. You cannot return anything from an async function. Check the question I marked as duplicate for more information – Rory McCrossan Sep 09 '16 at 15:07
Sorry, made a further change – nikjohn Sep 09 '16 at 15:08

Callback in ajax request

1 Answers1