AngularJs and SocketIo

Question

I need some help understanding the code below. It is taken from: http://www.html5rocks.com/en/tutorials/frameworks/angular-websockets

app.factory('socket', function ($rootScope) {
var socket = io.connect();
  return {
    on: function (eventName, callback) {
      socket.on(eventName, function () {  
        var args = arguments;
        $rootScope.$apply(function () {
          callback.apply(socket, args);
        });
      });
    },
    emit: function (eventName, data, callback) {
      socket.emit(eventName, data, function () {
        var args = arguments;
        $rootScope.$apply(function () {
          if (callback) {
            callback.apply(socket, args);
          }
        });
      })
    }
  };

I am having problem understanding:

From where did arguments come
what is callback.apply and what is it doing?

Pavlo · Accepted Answer · 2015-10-07 09:08:16Z

1

It's basic JavaScript, nothing to do with AngularJS or Socket.io.

arguments is a "magic" variable available inside every function to access it's arguments in array-like manner.

Function#apply is a way to call a function with a different this context providing arguments as the second argument.

answered Oct 7, 2015 at 9:08

Pavlo

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2 Comments

Sonali Gupta Over a year ago

Controller is this:

function AppCtrl($scope, socket) {    socket.on('init', function (data) {     $scope.name = data.name;     $scope.users = data.users;   });

Can you explain me the flow? I am not sure what callback.apply is invoking.

Pavlo Over a year ago

I believe the post answers your initial questions (if you agree, you can accept it). If you have more questions, feel free to create more posts.

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