Get the full call stack trace of $http calls

Question

Let\'s say someone wrote a method like this in a file called app.js trying to peform an XHR request angainst a non existing url:

app.controller(\'Ma         


        

Answer 1

So, you see, this issue is mostly because angular's $http sucks. Sorry about that.

Let's try to use the bluebird library, because it provides long stack traces.

Promise.longStackTraces();
Promise.resolve($http.get('...'));

You get the following stack trace:

Possibly unhandled Error: [object Object]
    at Promise$_rejectFromThenable (http://cdn.jsdelivr.net/bluebird/1.2.4/bluebird.js:4736:52)
    at wrappedErrback (https://code.angularjs.org/1.3.0-beta.5/angular.js:11334:78)
    at wrappedErrback (https://code.angularjs.org/1.3.0-beta.5/angular.js:11334:78)
    at wrappedErrback (https://code.angularjs.org/1.3.0-beta.5/angular.js:11334:78)
    at https://code.angularjs.org/1.3.0-beta.5/angular.js:11467:76
    at Scope.$eval (https://code.angularjs.org/1.3.0-beta.5/angular.js:12418:28)
    at Scope.$digest (https://code.angularjs.org/1.3.0-beta.5/angular.js:12230:31)
    at Scope.$apply (https://code.angularjs.org/1.3.0-beta.5/angular.js:12522:24)
    at done (https://code.angularjs.org/1.3.0-beta.5/angular.js:8207:45)
    at completeRequest (https://code.angularjs.org/1.3.0-beta.5/angular.js:8412:7) 

(Plunker here.)

The most important line is the first: Possibly unhandled Error: [object Object].

Yep. An object is thrown, not a real Error object, with the stack property attached to it. For the reference, here is how to throw an error and keep its stack along with it: https://github.com/Ralt/newerror/blob/master/index.js

So, how to fix this? It depends on several decisions:

• Do you want to add a proper Promise lib that enables long stack traces?
• Do you want to use another xhr lib that throws correct errors?

If you want to add a real Promise lib, use bluebird. AFAIK, it is one of the few that provides long stack traces, and it is the fastest one out there.

For a proper xhr lib that throws real errors, I'm afraid you're out of luck there. Writing a custom one with the support for browsers you want isn't really hard though. With no IE8 support, this works (with bluebird):

function xhr(url) {
    return new Promise(function(resolve, reject) {
        var xhr = new XMLHttpRequest();
        xhr.onload = function() {
            resolve(xhr.responseText);
        };
        xhr.onerror = reject;
        xhr.open('GET', url);
        xhr.send();
    });
}

(Plunker here.)

As you can see, the stack trace is informative:

Answer 2

XHR requests are stacked in $http.pendingRequests array and are send later. Which is why you can't find a direct linked between where $http is called and where the actual XHR request is made.

If you want to know which function called $http you have to set a breakpoint in $http function.

It kinds of defeat the whole "XHR breakpoints" purpose in my opinion.

Answer 3

One option that came in my mind is to create a module for $http debugging that you can add it as a dependency in your main module whenever you need to debug $http calls. There a decorator for the $http service can be registered that will simply log the arguments of the call a forward it to the $http service. There a breakpoint can be set too.

I have created a simple working example here. I hope it will help.

Example $http logger decorator implementation:

var httpDebugging = angular.module('http-debugging', []);

httpDebugging.decorator('$http', function ($delegate) {
  var debugAware = function (fnCallback) {
    return function () {
        var result = fnCallback.apply(this, arguments);    
        console.log('$http decorator: ', arguments);
        return result;
    };   
  }; 

  for(var prop in $delegate) {
    if (angular.isFunction($delegate[prop])) {
        $delegate[prop] = debugAware($delegate[prop]);
    }
  }

  return $delegate;
});