jquery deferred and return false based on server response

Question

I have the below jquery deferred logic.

var $qCallA = callA();
var $qCallB = callB();

$.when($qCallA,$qCallB).then(function () {
        $("#spinnerDiv").removeClass('spinner show');
});

function callA() {
    return $.getJSON("/callA", function (data) {
        if (data.status === "success") {
            buildTable1(data);
        }
    });
}

function callB() {
    return $.getJSON("/callB", function (data) {
        if (data.status === "success") {
            buildTable2(data);
        }
    });
}

I want to return false for $.getJSON call based on response from the backend json. For example , if the data.status == "failure" then I want to return "false" for getJSON . How to achieve this?

Thanks

You can't return anything from the async function. What exactly do you need to do when `data.status == 'failure'` happens? — Rory McCrossan, Nov 29 '16 at 13:50
You can not return from an asynchronous call.... Do you want to fail the promise? — epascarello, Nov 29 '16 at 13:51
@JavaUser What's with the bounty? Is anything missing from my answer, does it not work for you? — Bergi, Dec 11 '16 at 17:05

score 8 · Answer 1 · edited Dec 10 '16 at 14:34

Sounds like you want to use proper then callbacks, where you can return a new result value for the promise:

$.when(callA(), callB()).then(function(a, b) {
    $("#spinnerDiv").removeClass('spinner show');
    if (a && b) …
});

function callA() {
    return $.getJSON("/callA").then(function(data) {
        if (data.status === "success") {
            buildTable1(data);
        }
        return data.status != "failure";
    });
}

function callB() {
    return $.getJSON("/callB").then(function(data) {
        if (data.status === "success") {
            buildTable2(data);
        }
        return data.status != "failure";
    });
}

score 5 · Accepted Answer · edited Dec 10 '16 at 14:34

You should provide success callbacks then for your $.getJSON and return custom Deffered for $.when to handle.

That way you can manually resolve or reject based on data that's in the JSON.

var $qCallA = callA();
var $qCallB = callB();

$.when($qCallA,$qCallB).then(function (s1, s2) {
    $("#spinnerDiv").removeClass('spinner show');
}).fail(function() {
    //handle failure
});

function callA() {
    return $.getJSON("/callA").then(function (data) {
        if (data.status === 'failure') {
        return $.Deferred().reject("A: no success");
      }
      return $.Deferred().resolve(data);      
    });
}

function callB() {
    return $.getJSON("/callB").then(function (data) {
        if (data.status === 'success') {
        return $.Deferred().resolve(data);
      }
      return $.Deferred().reject("B: no success");
    });
}

Similar JSFiddle

jquery deferred and return false based on server response

2 Answers2