AngularJS : remove $rootScope from a service - angularjs

Question

I have a service wrapped around WebSocket, I wanted to do it with promises and coupling requests with responses, here is what I came up with:
(function () {
var app = angular.module('mainModule');
app.service('$wsService', ['$q', '$rootScope', '$window', function($q, $rootScope, $window) {
var self = this;
// Keep all pending requests here until they get responses
var callbacks = {};
// Create a unique callback ID to map requests to responses
var currentCallbackId = 0;
var ws = new WebSocket("ws://127.0.0.1:9090");
this.webSocket = ws;
ws.onopen = function(){
$window.console.log("WS SERVICE: connected");
};
ws.onmessage = function(message) {
listener(JSON.parse(message.data));
};
var listener = function (messageObj) {
// If an object exists with callback_id in our callbacks object, resolve it
if(callbacks.hasOwnProperty(messageObj.Request.ID)) {
$rootScope.$apply(
callbacks[messageObj.Request.ID].cb.resolve(messageObj));
delete callbacks[messageObj.Request.ID];
}
};
// This creates a new callback ID for a request
var getCallbackId = function () {
currentCallbackId += 1;
if(currentCallbackId > 10000) {
currentCallbackId = 0;
}
return currentCallbackId;
};
//sends a request
var sendRequest = function (request, callback) {
var defer = $q.defer();
var callbackId = getCallbackId();
callbacks[callbackId] = {
time: new Date(),
cb:defer
};
request.ID = callbackId;
$window.console.log("WS SERVICE: sending " + JSON.stringify(request));
ws.send(JSON.stringify(request));
if(typeof callback === 'function') {
defer.promise.then(function(data) {
callback(null, data);
},
function(error) {
callback(error, null);
});
}
return defer.promise;
};
this.exampleCommand = function(someObject, callback){
var promise = sendRequest(someObject, callback);
return promise;
};
}]);
}());
And I use it in a controller like so:
(function () {
'use strict';
var app = angular.module('mainModule');
app.controller('someController', ['$scope', '$wsService', function ($scope, $wsService) {
$scope.doSomething = function(){
$wsService.exampleCommand(
{/*some data for the request here*/},
function(error, message){
//do something with the response
}
);
};
}]);
}());
After implementing this, I have been told that the service should not really operate on any kind of scope. So my question is - how would I go about removing the $rootScope from the service? I am not even sure if I should get rid of it, and if the conventions say I should, how to approach it. Thanks

Answer 1

I have been told that the service should not really operate on any kind of scope.
Who told you that? It's completely wrong.
Your service is receiving callbacks outside of a digest cycle from the websocket. To work with angular, those updates need to be applied inside a digest cycle - this is exactly what you're doing.
For reference, see the built in $http service. That wraps XMLHttpRequest analogously to how you're wrapping web sockets and it depends on $rootScope for exactly the functionality your code depends on $rootScope for.
Your code demonstrates the canonical use of $rootScope inside a service.