emit() arguments

[jkirkwood]

I've been experiencing some strange problems when using the emit function with multiple data arguments.

For instance when I call

socket.emit('machines:getHwStatusUpdates', machineId, device, null,
  function(err, u) {...});

At the beginning of the emit function the arguments array looks as expected:

0: "machines:getHwStatusUpdates"
1: 16
2: "modem"
3: null
4: function (err, u) {

However, after var callback = arguments[lastIndex] is executed the arguments array is altered like this:

0: "machines:getHwStatusUpdates"
1: 16
2: function (err, u) {
3: null
4: function (err, u) {

It appears that callback defined in the function params still points to the arguments array during the function's execution, and is being updated by var callback = arguments[lastIndex].

Does this behavior make sense? Im using the latest version of Chrome on OS X.

What's strange is that I only have problems when I concat this file with my other js files. If I run this script without concating them, the arguments array is never altered.

Is this some strange js bug, or am I missing something here. Perhaps the parameters should be removed from the emit function altogether, since they are never referred to anyways? This seems to fix my problem:

emit: function () {
  var lastIndex = arguments.length - 1;
  var callback = arguments[lastIndex];
  if(typeof callback == 'function') {
    callback = asyncAngularify(socket, callback);
    arguments[lastIndex] = callback;
  }
  return socket.emit.apply(socket, arguments);
}

[btford]

@jkirkwood maybe submit a PR with this change plus a test case?

Is this possibly because of a "use strict"?

[jkirkwood]

Ah, that's it. From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode#Making_eval_and_arguments_simpler:

Second, strict mode code doesn't alias properties of arguments objects created within it. In normal code within a function whose first argument is arg, setting arg also sets arguments[0], and vice versa (unless no arguments were provided or arguments[0] is deleted). arguments objects for strict mode functions store the original arguments when the function was invoked. arguments[i] does not track the value of the corresponding named argument, nor does a named argument track the value in the corresponding arguments[i].

When I concat my js files, angular.js is at the top which starts with:

/**
 * @license AngularJS v1.2.16
 * (c) 2010-2014 Google, Inc. http://angularjs.org
 * License: MIT
 */
(function(window, document, undefined) {'use strict';

so 'use strict' is in the function scope, and not applied globally because it is not the first statement.

Should angular-socket-io also be modified to declare 'use strict' on the function scope? Like so?

angular.module('btford.socket-io', []).
  provider('socketFactory', function () {
    'use strict';
    ...

[btford]

Yep. would you like to put together a PR?

[btford]

Fixed in #55.