AngularJS $http function always returning undefined when returning

Question

var bar = dataService.makeHttpRequest("GET", "/documents/checkfilename/", null,
            function (data, status, headers, config) {
                // I can see `true` if I alert(data); here
                // I want to return the contents of data because
                // it's a true/false and would perform tasks based
                // on it being true or false.

                return data;
            });

alert(bar); // this should alert `true` or `false` but is `undefined`

Why does alert(bar) always return undefined? I know that data in the above function has true or false, I am able to alert it; but, I want to return it and do things only when it is true.

The dataService.makeHttpRequest service function looks like the following:

dataService.makeHttpRequest = function(requestType, urlString, dataObject, successFunc, errorFunc) {
    $http({
        method:requestType, 
        url:$rootScope.serverAddress+urlString,
        data:dataObject
        })
        .success(successFunc)
        .error(errorFunc);
};

The callback you are passing is executed after the HTTP request, so bar is just the return of the function makeHttpRequest which doesn't return anything so you're getting undefined. — GillesC
– GillesC, Commented May 20, 2015 at 20:11

ach · Accepted Answer · 2015-05-20 20:25:46Z

The simplest explanation for why your method makeHttpRequest is returning undefined is that, well, it doesn't actually return a value (where's the return statement?)

However, even if you were returning the result of the call to $http it wouldn't be what you want. The whole point of a callback is to handle an asynchronous operation -- if you want to perform logic based on data received from the HTTP response, it must be done in the callback itself.

Since $http() returns a promise, a cleaner way to do what you want to do would be:

dataService.makeHttpRequest = function(requestType, urlString, dataObject) {
    return $http({
        method:requestType, 
        url:$rootScope.serverAddress+urlString, //recommend taking this as a parameter instead of abusing $rootScope
        data:dataObject
    });
};

dataService.makeHttpRequest("GET", "/documents/checkfilename/", null).success(function (data, status, headers, config) {
     //do whatever you want with "data" here
}); //can also chain ".error" here to specify an error callback

yep that's the right answer. although there are cases when you need a $q to time several asynchronous request, even when they are $http

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