Angularjs socket.io service

Question

Hi I'm building an angularjs service that will use websockets via socket.io to communicate with backend (node.js). I found a snippet of code online but I don't quite understand how it works. Specifically on the lines under "var args = arguments". Help?

angularjs_service.js

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);
          }
        });
      })
    }
  };
});

C Fairweather · Accepted Answer · 2014-01-27 03:49:45Z

3

This is where javascript betrays its aversion to unnamed variables. The variable arguments refers to an array of arguments that are passed in to a function. What you see there is angular code grabbing an array of the function's arguments and passing them to apply.

function(myVar1, myVar2){
    console.log(arguments.length);
}

Would output 2.

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/arguments

answered Jan 27, 2014 at 3:49

C Fairweather

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3 Comments

user1424508 Over a year ago

ok thanks. How about $rootScope.$apply(function () { callback.apply(socket, args); }); What are these lines doing?

C Fairweather Over a year ago

This framework is well documented on the angular website, since it is an angular specific question. docs.angularjs.org/api/ng.$rootScope.Scope

C Fairweather Over a year ago

If this has answered your question, I would appreciate if you accepted it! :D

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