How to cancel an $http request in AngularJS?

Question

Given a Ajax request in AngularJS

$http.get("/backend/").success(callback);

what is the most effective way to cancel that request if another request is launched (same backend, different parameters for instance).

Answer 1

here is a version that handles multiple requests, also checks for cancelled status in callback to suppress errors in error block. (in Typescript)

controller level:

    requests = new Map<string, ng.IDeferred<{}>>();

in my http get:

    getSomething(): void {
        let url = '/api/someaction';
        this.cancel(url); // cancel if this url is in progress

        var req = this.$q.defer();
        this.requests.set(url, req);
        let config: ng.IRequestShortcutConfig = {
            params: { id: someId}
            , timeout: req.promise   // <--- promise to trigger cancellation
        };

        this.$http.post(url, this.getPayload(), config).then(
            promiseValue => this.updateEditor(promiseValue.data as IEditor),
            reason => {
                // if legitimate exception, show error in UI
                if (!this.isCancelled(req)) {
                    this.showError(url, reason)
                }
            },
        ).finally(() => { });
    }

helper methods

    cancel(url: string) {
        this.requests.forEach((req,key) => {
            if (key == url)
                req.resolve('cancelled');
        });
        this.requests.delete(url);
    }

    isCancelled(req: ng.IDeferred<{}>) {
        var p = req.promise as any; // as any because typings are missing $$state
        return p.$$state && p.$$state.value == 'cancelled';
    }

now looking at the network tab, i see that it works beatuifully. i called the method 4 times and only the last one went through.

Answer 2

If you want to cancel pending requests on stateChangeStart with ui-router, you can use something like this:

// in service

                var deferred = $q.defer();
                var scope = this;
                $http.get(URL, {timeout : deferred.promise, cancel : deferred}).success(function(data){
                    //do something
                    deferred.resolve(dataUsage);
                }).error(function(){
                    deferred.reject();
                });
                return deferred.promise;

// in UIrouter config

$rootScope.$on('$stateChangeStart', function (event, toState, toParams, fromState, fromParams) {
    //To cancel pending request when change state
       angular.forEach($http.pendingRequests, function(request) {
          if (request.cancel && request.timeout) {
             request.cancel.resolve();
          }
       });
    });

Answer 3

You can add a custom function to the $http service using a "decorator" that would add the abort() function to your promises.

Here's some working code:

app.config(function($provide) {
    $provide.decorator('$http', function $logDecorator($delegate, $q) {
        $delegate.with_abort = function(options) {
            let abort_defer = $q.defer();
            let new_options = angular.copy(options);
            new_options.timeout = abort_defer.promise;
            let do_throw_error = false;

            let http_promise = $delegate(new_options).then(
                response => response, 
                error => {
                    if(do_throw_error) return $q.reject(error);
                    return $q(() => null); // prevent promise chain propagation
                });

            let real_then = http_promise.then;
            let then_function = function () { 
                return mod_promise(real_then.apply(this, arguments)); 
            };

            function mod_promise(promise) {
                promise.then = then_function;
                promise.abort = (do_throw_error_param = false) => {
                    do_throw_error = do_throw_error_param;
                    abort_defer.resolve();
                };
                return promise;
            }

            return mod_promise(http_promise);
        }

        return $delegate;
    });
});

This code uses angularjs's decorator functionality to add a with_abort() function to the $http service.

with_abort() uses $http timeout option that allows you to abort an http request.

The returned promise is modified to include an abort() function. It also has code to make sure that the abort() works even if you chain promises.

Here is an example of how you would use it:

// your original code
$http({ method: 'GET', url: '/names' }).then(names => {
    do_something(names));
});

// new code with ability to abort
var promise = $http.with_abort({ method: 'GET', url: '/names' }).then(
    function(names) {
        do_something(names));
    });

promise.abort(); // if you want to abort

By default when you call abort() the request gets canceled and none of the promise handlers run.

If you want your error handlers to be called pass true to abort(true).

In your error handler you can check if the "error" was due to an "abort" by checking the xhrStatus property. Here's an example:

var promise = $http.with_abort({ method: 'GET', url: '/names' }).then(
    function(names) {
        do_something(names));
    }, 
    function(error) {
        if (er.xhrStatus === "abort") return;
    });

Answer 4

This feature was added to the 1.1.5 release via a timeout parameter:

var canceler = $q.defer();
$http.get('/someUrl', {timeout: canceler.promise}).success(successCallback);
// later...
canceler.resolve();  // Aborts the $http request if it isn't finished.

Answer 5

Cancelation of requests issued with $http is not supported with the current version of AngularJS. There is a pull request opened to add this capability but this PR wasn't reviewed yet so it is not clear if its going to make it into AngularJS core.

Answer 6

This enhances the accepted answer by decorating the $http service with an abort method as follows ...

'use strict';
angular.module('admin')
  .config(["$provide", function ($provide) {

$provide.decorator('$http', ["$delegate", "$q", function ($delegate, $q) {
  var getFn = $delegate.get;
  var cancelerMap = {};

  function getCancelerKey(method, url) {
    var formattedMethod = method.toLowerCase();
    var formattedUrl = encodeURI(url).toLowerCase().split("?")[0];
    return formattedMethod + "~" + formattedUrl;
  }

  $delegate.get = function () {
    var cancelerKey, canceler, method;
    var args = [].slice.call(arguments);
    var url = args[0];
    var config = args[1] || {};
    if (config.timeout == null) {
      method = "GET";
      cancelerKey = getCancelerKey(method, url);
      canceler = $q.defer();
      cancelerMap[cancelerKey] = canceler;
      config.timeout = canceler.promise;
      args[1] = config;
    }
    return getFn.apply(null, args);
  };

  $delegate.abort = function (request) {
    console.log("aborting");
    var cancelerKey, canceler;
    cancelerKey = getCancelerKey(request.method, request.url);
    canceler = cancelerMap[cancelerKey];

    if (canceler != null) {
      console.log("aborting", cancelerKey);

      if (request.timeout != null && typeof request.timeout !== "number") {

        canceler.resolve();
        delete cancelerMap[cancelerKey];
      }
    }
  };

  return $delegate;
}]);
  }]);

WHAT IS THIS CODE DOING?

To cancel a request a "promise" timeout must be set. If no timeout is set on the HTTP request then the code adds a "promise" timeout. (If a timeout is set already then nothing is changed).

However, to resolve the promise we need a handle on the "deferred". We thus use a map so we can retrieve the "deferred" later. When we call the abort method, the "deferred" is retrieved from the map and then we call the resolve method to cancel the http request.

Hope this helps someone.

LIMITATIONS

Currently this only works for $http.get but you can add code for $http.post and so on

HOW TO USE ...

You can then use it, for example, on state change, as follows ...

rootScope.$on('$stateChangeStart', function (event, toState, toParams) {
  angular.forEach($http.pendingRequests, function (request) {
        $http.abort(request);
    });
  });