How to send an HTTP request onbeforeunload in AngularJS?

Question

I have a simple angular app that has two views that are loaded using ngRoute. I need to do some clean up on the server when the user navigates between views and when the user leaves the page (refreshes window, closes tab, or closes browser).

My first stop was here: Showing alert in angularjs when user leaves a page. It solved the first case where the user navigates between views. I've handled the clean up like this:

$scope.$on('$locationChangeStart', function (event) {
    var answer = confirm("Are you sure you want to leave this page?")
    if (answer) {
        api.unlock($scope.id); //api is a service that I wrote. It uses angular $http service to handle communications and works in all other cases.
    } else {
        event.preventDefault();
    }
});

However, I haven't been able to handle the case where the user leaves the page. Following the above answer and this Google Groups post: https://groups.google.com/forum/#!topic/angular/-PfujIEdeCY I tried this:

window.onbeforeunload = function (event) {
    api.unlock($scope.id); //I don't necessarily need a confirmation dialogue, although that would be helpful. 
};

But it did not work. Then I've read here: How to execute ajax function onbeforeunload? that the request needs to be synchronous and here: How to $http Synchronous call with AngularJS that Angular does not support this (although this one might be outdated).

I've also tried calling $http directly (without the service) but that did not work either. At this point I'm stuck. Any suggestions / leads would be really appreciated.

Thanks in advance!

Answer 1

The problem is that angular always make ASYNCHRONOUS calls with the $http service (and you can’t change that behavior). Since the page exits before the $http service have a chance to emit the requests you are not getting the desired result.

If you want a workarround without using any third party libraries try the following code:

var onBeforeUnload = function () {

    var data = angular.toJson($scope.id...);//make sure you $scope is legal here...
    var xmlhttp = new XMLHttpRequest();
    xmlhttp.open("POST", "apiURL/unlock", false);//the false is for making the call synchronous
    xmlhttp.setRequestHeader("Content-type", "application/json");
    xmlhttp.setRequestHeader("Authorization", token);
    xmlhttp.send(data);
}

It will block UI until the request is completed, so try to make the server fast or the user will notice.