How to sequentially execute functions using angularjs

app.controller("myctrl", function ($scope, $timeout, $filter, $q ) {

$scope.abc = function()
{

function isPromiseLike(obj) {
return obj && angular.isFunction(obj.then);
}
serial({ task1, task2 });

function serial(tasks) {
var prevPromise;
var error = new Error();
angular.forEach(tasks, function (task, key) {
var success = task.success || task;
var fail = task.fail;
var notify = task.notify;
var nextPromise;

//First task
if (!prevPromise) {
nextPromise = success();
if (!isPromiseLike(nextPromise)) {
error.message = "Task " + key + " did not return a promise.";
throw error;
}
}
else
{
//Wait until the previous promise has resolved or rejected to execute the next task

nextPromise = prevPromise.then(
/*success*/function (data) {
if (!success) { return data; }
var ret = success(data);
if (!isPromiseLike(ret)) {
error.message = "Task " + key + " did not return a promise.";
throw error;
}
return ret;
},
/*failure*/function (reason) {
if (!fail) { return $delegate.reject(reason); }
var ret = fail(reason);
if (!isPromiseLike(ret)) {
error.message = "Fail for task " + key + " did not return a promise.";
throw error;
}
return ret;
},
notify);
}
prevPromise = nextPromise;
});

return prevPromise || $delegate.when();
}


function task1() {

var d = $q.defer();
$timeout(function () {
//some task

d.resolve();
}, 1000);
return d.promise;
}

function task2() {

var d = $q.defer();
$timeout(function () {
//some task

d.resolve();
}, 1000);
return d.promise;
}
}
});

cordova app goes white screen when using $q.defer in angularjs.It works fine when running in ripple but not working in device.