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javascript module How to get the current object ( this referencing something else )?

I'm noticing that this references something else inside a function that I added as event listener. I read this informative resource and a few questions on stackoverflow but I don't know how to apply it to my case (I'm quite new to the "oop" and the module pattern in javascript so I'm a bit lost).
Here is my little module:
var myModule = myModule || ( function() {
// Adds event listener for all browsers
// see http://stackoverflow.com/a/6348597
function addEvent( element, event, listener ) {
// IE < 9 has only attachElement
// IE >= 9 has addEventListener
if ( element.addEventListener ) {
return element.addEventListener( event, listener, false );
} else if ( element.attachElement ) {
return element.attachElement( "on" + event, listener );
}
}
return {
init: function() {
// Add event listeners
addEvent(
document.getElementById( "myElementId" ),
"click",
this.processMyElement
);
addEvent(
document.getElementById( "myOtherElementId" ),
"click",
this.processMyOtherElement
);
},
hideElementById: function( elementId ) {
document.getElementById( elementId ).style.display = "none";
},
showElementById: function( elementId ) {
document.getElementById( elementId ).style.display = "block";
},
processMyElement: function() {
this.hideElementById( "myElementId" );
this.showElementById( "myOtherElementId" );
},
processMyOtherElement: function() {
// Do something else...
}
};
}() );
The thing is that this which I use to call hideElementById in processMyElement is referencing to the element I added an eventListener to, and not to the current object.
I tried a few things without success:
removing the return in addEvent,
using var that = this as a private property of the module (placed in the module before the addEvent definition) and using that in processMyElement
using apply in the init method but it (obviously) calls processMyElement when adding the listener to the element
Could anyone help me with this? I tried a few things but I cannot see how to do it better...
PS: I try to build testable code, that's why I had those hideElementById and showElementById methods, in order to separate various functionalities (that may be quite clumsy actually but that's where I am ATM...).

There are (more than) a couple of common ways to get the correct this binding. For example, you can use a closure:
var that = this;
addEvent(
document.getElementById( "myOtherElementId" ),
"click",
function () {
that.processMyOtherElement();
}
);
Or you could use bind:
addEvent(
document.getElementById( "myOtherElementId" ),
"click",
this.processMyOtherElement.bind(this)
);
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_objects/Function/bind
The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.
Which one you use would depend on other factors.

Accessing a jQuery element reference as an object property

I'm trying to set an element as a property of an object using jQuery. When I make a direct reference to the jquery object, it works, however when I make the reference through the calculator object, it doesn't.
How do I fix this?
var calculator = {
settings: {
displayNumber: $('.dispNumber'),
modNumber: $('.modNumber')
}
}
window.onload = function(){
console.log( $('.dispNumber').html() ); //this one works
console.log( calculator.settings.displayNumber.html() ); //this one doesn't
}

If calculator.settings.displayNumber isn't created in a dom ready scope, it won't have the elements.

Since you are using jQuery, you should put everything handling the DOM inside either :
$(function() {
//code here will always run after the DOM is ready.
var calculator = {
settings: {
displayNumber: $('.dispNumber'),
modNumber: $('.modNumber')
}
};
console.log( $('.dispNumber').html() ); //this one works
console.log( calculator.settings.displayNumber.html() ); //this one doesn't
});
OR
simply add <script>........code.......</script> before your </body>.
The first one is the proper way to handle DOM-related operations.
Edit: reusable object :
var Calculator = function($) {
this.settings = {
displayNumber: $('.dispNumber'),
modNumber: $('.modNumber')
};
};
Calculator.prototype = {
log: function() {
console.log(this.settings.displayNumber.html());
console.log(this.settings.modNumber.html());
}
}
$(function(){
var calculator = new Calculator($);
calculator.log();
console.log(calculator.settings.displayNumber.html());
});

Your code works fine. The only reasons why it shouldn't work is that calculator is not instanciated before window.onload.
Remove that issue and everything works. See: http://jsfiddle.net/352Cm/
var calculator = {
settings: {
displayNumber: $('.dispNumber'),
modNumber: $('.modNumber')
}
}
console.log( $('.dispNumber').html() ); //this one works
console.log( calculator.settings.displayNumber.html() ); //this one doesn't
Try to console.log(calculator) in window.load and you'll probably see 'undefined' or crashing code.

Using sinon.js spy() to wrap an existing function

I'm new to JavaScript testing and have run across a problem when trying to use sinon.js to spy on existing functions.
Let's say I have a function called
nsClientInfectionControlIndex.handleEditButton();
which looks like
var nsClientInfectionControlIndex = {
showQtipError : function (message)
{
///<summary>Shows qTip error on edit button</summary>
///<param name="message">The text message to be displayed</param>
$( "#editBtn" ).qtip( nsCBS.ErrorTip( message ) ).qtip( "show" );
},
goToEditPage : function (id)
{
/// <summary>Navigates browser window to edit page</summary>
/// <param name="id">The data-id (Client Infection Control Id) attribute from selected row</param>
var url = '/ClientInfectionControl/ClientInfectionControl/'
window.location.href = url + "?id=" + id;
},
handleEditButton: function () {
var id = $( ".selectedRow" ).attr( "data-id" );
if ( id != null ) {
nsClientInfectionControlIndex.goToEditPage( id );
} else {
nsClientInfectionControlIndex.showQtipError( "Please select a Client Infection Control Note first." );
}
},
};
Now in my test.js I used the following code
var errorSpy = sinon.spy( nsClientInfectionControlIndex.showQtipError );
//Act
nsClientInfectionControlIndex.handleEditButton();
//Assert
equal( errorSpy.called, true, "test" );
And the test fails (returns a false) although I would expect a true because the nsClientInfectionControlIndex.showQtipError is called.
Although as far as I understand the Sinon documentation I'm spying on my function correctly by including the function in the constructor. http://sinonjs.org/docs/#sinonspy
I can get it to work correctly if I approach the spy this way,
var errorSpy = sinon.spy();
nsClientInfectionControlIndex.showQtipError = errorSpy;
//Act
nsClientInfectionControlIndex.handleEditButton();
//Assert
equal( errorSpy.called, true, "test" );
However this replaces the original method functionality. Am I approaching this incorrectly? Any help would be appreciated.

When spying on object functions you must provide the object and function name separately rather than the actual function. This allows Sinon to replace the real function with the spy.
var errorSpy = sinon.spy( nsClientInfectionControlIndex, "showQtipError" );
Warning: If any code stores the function into a variable before setting up the spy, it will bypass the spy.
// before test runs
var callback = nsClientInfectionControlIndex.showQtipError;
// in test
var errorSpy = ...
// activated by test
callback(); <-- bypasses spy

Unbind an Anonymous Function

Can somebody tell how to "unbind" an anonymous function?
In jQuery it's capable to do that, but how can I implement this Functionality in my own script.
This is the scenario:
The following code attach a onclick event to the Div which have someDivId as ID, now when you click the DIV, it's showing 'clicked!'.
var a = document.getElementById('someDivId');
bindEvent(a,'click',function(){alert('clicked!');});
That's all great, the problem is how to "un-attach" the Function to the DIV if the function is anonymous or how to "un-attach" all attached events to the 'a' Element?
unBind(a,'click'); //Not necessarily the given params, it's just an example.
This is the code for bindEvent Method:
function bindEvent (el,evtType,fn){
if ( el.attachEvent ) {
el['e'+evtType+fn] = fn;
el[evtType+fn] = function(){
fn.call(el,window.event);
}
el.attachEvent( 'on'+evtType, el[evtType+fn] );
} else {
el.addEventListener( evtType, fn, false );
}
}

Finally, and after hours of Test&Errors i have found a solution, maybe it's not the best or most efficient but... IT WORKS! (Tested on IE9, Firefox 12, Chrome 18)
First all I'v create two cross-browser and auxiliary addEvent() and removeEvent() methods. (Idea taken from Jquery's source code!)
HELPERS.removeEvent = document.removeEventListener ?
function( type, handle,el ) {
if ( el.removeEventListener ) {
//W3C Standard
el.removeEventListener( type, handle, true );
}
} :
function( type, handle,el ) {
if ( el.detachEvent ) {
//The IE way
el.detachEvent( 'on'+type, el[type+handle] );
el[type+handle] = null;
}
};
HELPERS.addEvent = document.addEventListener ?
function( type, handle,el ) {
if ( el.addEventListener ) {
//W3C Standard
el.addEventListener( type, handle, true );
}
} :
function( type, handle,el ) {
if ( el.attachEvent ) {
//The IE way
el['e'+type+handle] = handle;
el[type+handle] = function(){
handle.call(el,window.event);
};
el.attachEvent( 'on'+type, el[type+handle] );
}
}
Also we need some kind of 'container' to store the attached events to elements, like this:
HELPERS.EVTS = {};
And finally the two callable and exposed to the users Methods:
The next one to add an Event(event) and associate this Event to a Method (handler) for a specific Element (el).
function bindEvent(event, handler,el) {
if(!(el in HELPERS.EVT)) {
// HELPERS.EVT stores references to nodes
HELPERS.EVT[el] = {};
}
if(!(event in HELPERS.EVT[el])) {
// each entry contains another entry for each event type
HELPERS.EVT[el][event] = [];
}
// capture reference
HELPERS.EVT[el][event].push([handler, true]);
//Finally call the aux. Method
HELPERS.addEvent(event,handler,el);
return;
}
Lastly the method that un-attach every pre-attached events (event) for an specific Element (el)
function removeAllEvent(event,el) {
if(el in HELPERS.EVT) {
var handlers = HELPERS.EVT[el];
if(event in handlers) {
var eventHandlers = handlers[event];
for(var i = eventHandlers.length; i--;) {
var handler = eventHandlers[i];
HELPERS.removeEvent(event,handler[0],el);
}
}
}
return;
}
By the way, to call this methods you must do the following:
Capture a DOM Node
var a = document.getElementById('some_id');
Call the method 'bindEvent()' with the corresponding parameters.
bindEvent('click',function(){alert('say hi');},a);
And to de-attach it:
removeAllEvent('click',a);
That's all, hope will be useful for somebody one day.

Personally (and I know this isn't the "best" way, as it does require me to think about what I'm doing), I like to just use the on* event properties of the element I'm working with.
This has the convenient upside of being able to quickly and easily detach events.
var a = document.getElementById('someDivId');
a.onclick = function() {alert("Clicked!");};
// later...
a.onclick = null;
However, you do have to be careful with this because if you try to add a second event handler it will overwrite the first. Keep that in mind and you should be all fine.

I'm not sure if you can unbind an anonymous function attached via javascript. If possible you can simple remove the element from the DOM and recreate it. This will get rid of any event handlers previously attached.

JavaScript provides no list of event listeners attached to a node.
You can remove all event listeners of a node but using the Node.cloneNode method, see here: https://developer.mozilla.org/En/DOM/Node.cloneNode
This clones the node (obviously) but it does not clone the event listeners attached to it.
You could also just bind empty functions as event listeners:
function noop() {}
bindEvent(myElement, "click", noop);

This is from jquery's source:
jQuery.removeEvent = document.removeEventListener ?
function( elem, type, handle ) {
if ( elem.removeEventListener ) {
elem.removeEventListener( type, handle, false );
}
} :
function( elem, type, handle ) {
if ( elem.detachEvent ) {
elem.detachEvent( "on" + type, handle );
}
};

"this" doesn't work when binding functions to events inside a Javascript class

First off, I know I can copy "this" on instantiation, but that doesn't work here.
Basically I'm writing something to track people interacting with Youtube videos.
I got this working fine for one video at a time. But I want it to work on pages with multiple Youtube videos as well, so I converted the code to a class so I can create a new instance of it for each video on the page.
The problem is when trying to bind to the Youtube event listener for state changes. For "non-class" code, it looks like this:
var o = document.getElementById( id );
o.addEventListener("onStateChange", "onPlayerStateChange" );
(onPlayerStateChange being the function I wrote to track state changes in the video)
(I'm also aware that addEventListener won't work with MSIE but I'm not worrying about that yet)
But when I'm inside a class, I have to use "this" to refer to another function in that class. Here's what the code looks like:
this.o = document.getElementById( id );
this.o.addEventListener("onStateChange", "this.onPlayerStateChange" );
When it's written like this, this.onPlayerStateChange is never called. I've tried copying "this" into another variable, e.g. "me", but that doesn't work either. The onPlayerStateChange function is defined within the "this" scope before I do this:
var me = this;
this.o = document.getElementById( id );
this.o.addEventListener("onStateChange", "me.onPlayerStateChange" );
Any insights?
Looking through other similar questions here, all of them are using jQuery, and I think doing it that way might work if I did it that way. But I don't want to use jQuery, because this is going to be deployed on random third party sites. I love jQuery but I don't want it to be a requirement to use this.

You need a global way to access the onPlayerStateChange method of your object. When you assign me as var me = this;, the variable me is only valid inside the object method where it is created. However, the Youtube player API requires a function that is accessible globally, since the actual call is coming from Flash and it has no direct reference to your JavaScript function.
I found a very helpful blog post by James Coglan in which he discussed a nice way to communicate with the Youtube's JavaScript API and manage events for multiple videos.
I have released a JavaScript wrapper library using his ideas at http://github.com/AnuragMishra/YoutubePlayer. Feel free to checkout the code. The underlying idea is simple - store all instances of the player object on the constructor. For example:
function Player(id) {
// id of the placeholder div that gets replaced
// the <object> element in which the flash video resides will
// replace the placeholder div and take over its id
this.id = id;
Player.instances.push(this);
}
Player.instances = [];
When passing a string as a callback, use a string of the form:
"Player.dispatchEvent('playerId')"
When the flash player evals this string, it should return a function. That function is the callback that will ultimately receive the playback event id.
Player.dispatchEvent = function(id) {
var player = ..; // search player object using id in "instances"
return function(eventId) { // this is the callback that Flash talks to
player.notify(eventId);
};
};
When the flash player has loaded the video, the global onYoutubePlayerReady function is called. Inside that method, setup the event handlers for listening to playback events.
function onYouTubePlayerReady(id) {
var player = ..; // find player in "instances"
// replace <id> with player.id
var callback = "YoutubePlayer.dispatchEvent({id})";
callback = callback.replace("{id}", player.id);
player.addEventListener('onStateChange', callback);
}
See a working example here..

You can use a technique called currying to achieve this. For that you need a currying function. Here's one I wrote some time back
/**
* Changes the scope of function "fn" to the "scope" parameter specified or
* if not, defaults to window scope. The scope of the function determines what
* "this" inside "fn" evaluates to, inside the function "fn". Any additional arguments
* specified in this are passed to the underlying "curried" function. If the underlying
* function is already passed some arguments, the optional arguments are appended
* to the argument array of the underlying function. To explain this lets take
* the example below:
*
* You can pass any number of arguments that are passed to the underlying (curried)
* function
* #param {Function} fn The function to curry
* #param {Object} scope The scope to be set inside the curried function, if
* not specified, defaults to window
* #param arguments {...} Any other optional arguments ot be passed to the curried function
*
*/
var curry = function(fn, scope /*, arguments */) {
scope = scope || window;
var actualArgs = arguments;
return function() {
var args = [];
for(var j = 0; j < arguments.length; j++) {
args.push(arguments[j]);
}
for(var i = 2; i < actualArgs.length; i++) {
args.push(actualArgs[i]);
}
return fn.apply(scope, args);
};
};
You can use it to curry other functions and maintain the 'this' scope inside the functions.
Check out this article on currying
this.o.addEventListener("onStateChange", curry(onPlayerStateChange, this));
Edit:
var curriedFunc = curry(onPlayerStateChange, this);
this.o.addEventListener("onStateChange", "curriedFunc");
Edit:
Okay lets say this is your custom class you create:
function MyCustomClass() {
var privateVar = "x"; // some variables;
this.onPlayerStateChange = function() { //instance method on your custom class
// do something important
}
}
On a global level you create an instance of MyCustomClass
var myCustom = new MyCustomClass(); // create a new instance of your custom class
var curriedFunc = curry(myCustom.onplayerStageChange, myCustom); // curry its onplayerstateChange
// now add it to your event handler
o.addEventListener("onStateChange", "curriedFunc");

You should be using the following to attach an event:
this.o.addEventListener("statechange", this.onPlayerStateChange);
For addEventListener, you don't need to add the on prefix.
What I posted above is correct for standard javascript, but because this passes it to the YT flash object, it's expecting onStateChange which is correct.
HTH
EDIT: Try the method in this post to help.

TheCloudlessSky was partly right and Sean was partly right. You can continue to use "onStateChange" as the event name, but don't put this.onPlayerStateChange in quotations - doing so removes the special meaning of this and javascript will look for a function named "this.onPlayerStateChange" rather than looking for a function "onPlayerStateChange" within this object.
this.o.addEventListener("onStateChange", this.onPlayerStateChange);

After looking at the Youtube Api, it looks like the addEventListener only accepts a String for the event handler function. That means there's no clean way to register a unique event handler for each object.
An alternative is to register a global handler for all youtube state changes, and then let that handler pass the state change onto all your objects. Assuming you have an array of "tracker" objects:
function globalOnPlayerStateChange() {
for (tracker in myTrackerObjects) {
tracker.playerStateChange();
}
}
Each tracker object can then figure out by itself whether or not a state change actually occured (using the API's getPlayerState function):
function MyYoutubeTracker() {
this.currentState = ...
// Determine if state changed happened or not
this.playerStateChange = function() {
var newState = this.o.getPlayerState();
if (newState != this.currentState) {
// State has changed
this.currentState = newState;
}
}
// Register global event handler for this youtube object
this.o.addEventListener("onStateChange", "globalOnPlayerStateChange");
}

Ok, I got this all working. It's a bit of an ugly hack but it works. Basically I'm storing each new instance of the class in an array, and I'm passing the array key (1, 2, etc) into the class, so it can refer to itself externally as needed in a few key places.
The places I need the class to refer to itself externally are the string I pass to addEventListener, and within a few setTimeout functions, where "this" apparently loses its context (as far as I can tell anyways, because the only way I could them working was changing "this" to use external references instead.
Here's the full code.
On the page that has Youtube videos, they are injected using swfobject. The _ytmeta object stores the titles for each video. It's optional, but it's the only way to log the title of a video, because Youtube's API does not give it to you. This means you have to know the title up front, but the point is simply that if you want the title to show up in our reports, you have to create this object:
<div id='yt1'></div>
<script src='youtube.js'></script>
<script src='swfobject.js'></script>
<script>
var _ytmeta = {}
_ytmeta.yt1 = { 'title': 'Moonwalking in Walmart' };
var params = { allowScriptAccess: "always" };
swfobject.embedSWF("http://www.youtube.com/v/gE1ZvCnwkYk?enablejsapi=1&playerapiid=yt1", "yt1", "425", "356", "8", null, null, params );
</script>
So we're including the swfobject javascript code, as well as the youtube.js file, which will be hosted on our server and included on the pages you want to track videos.
Here are the contents of youtube.js:
// we're storing each youtube object (video) in an array, and passing the array key into the class, so the class instance can refer to itself externally
// this is necessary for two reasons
// first, the event listener function we pass to Youtube has to be globally accessible, so passing "this.blah" doesn't work
// it has to be passed as a string also, so putting "this" in quotes makes it lose its special meaning
// second, when we create timeout functions, the meaning of "this" inside that function loses its scope, so we have to refer to the class externally from there too.
// _yt is the global youtube array that stores each youtube object. yti is the array key, incremented automatically for each new object created
var _yt = [], _yti = 0;
// this is the function the youtube player calls once it's loaded.
// each time it's called, it creates a new object in the global array, and passes the array key into the class so the class can refer to itself externally
function onYouTubePlayerReady( id ) {
_yti++;
_yt[ _yti ] = new _yta( id, _yti );
}
function _yta( id, i ) {
if( !id || !i ) return;
this.id = id;
this.mytime;
this.scrubTimer;
this.startTimer;
this.last = 'none';
this.scrubbing = false;
this.o = document.getElementById( this.id );
this.o.addEventListener("onStateChange", "_yt["+i+"].onPlayerStateChange" );
this.onPlayerStateChange = function( newState ) {
// some events rely on a timer to determine what action was performed, we clear it on every state change.
if( this.myTime != undefined ) clearTimeout( this.myTime );
// pause - happens when clicking pause, or seeking
// that's why a timeout is used, so if we're seeking, once it starts playing again, we log it as a seek and kill the timer that would have logged the pause
// we're only giving it 2 seconds to start playing again though. that should be enough for most users.
// if we happen to log a pause during the seek - so be it.
if( newState == '2' ) {
this.myTime = setTimeout( function() {
_yt[i].videoLog('pause');
_yt[i].last = 'pause';
_yt[i].scrubbing = false;
}, 2000 );
if( this.scrubbing == false ){
this.last = 'pre-scrub';
this.scrubbing = true;
}
}
// play
else if( newState == '1' ) {
switch( this.last ) {
case 'none':
this.killTimers();
this.startTimer = setInterval( this.startRun, 200 );
break;
case 'pause':
this.myTime = setTimeout( function() {
_yt[i].videoLog('play');
_yt[i].last = 'play';
}, 2000 );
break;
case 'pre-scrub':
this.killTimers();
this.scrubTimer = setInterval( this.scrubRun, 200 );
break;
}
}
// end
else if( newState == '0' ) {
this.last = 'none';
this.videoLog('end');
}
}
// have to use external calls here because these are set as timeouts, which makes "this" change context (apparently)
this.scrubRun = function() {
_yt[i].videoLog('seek');
_yt[i].killTimers();
_yt[i].last = 'scrub';
_yt[i].scrubbing = false;
}
this.startRun = function() {
_yt[i].videoLog('play');
_yt[i].killTimers();
_yt[i].last = 'start';
}
this.killTimers = function() {
if( this.startTimer ) {
clearInterval( this.startTimer );
this.startTimer = null;
}
if( this.scrubTimer ){
clearInterval( this.scrubTimer );
this.scrubTimer = null;
}
}
this.videoLog = function( action ) {
clicky.video( action, this.videoTime(), this.videoURL(), this.videoTitle());
}
this.videoTime = function() {
return Math.round( this.o.getCurrentTime() );
}
this.videoURL = function() {
return this.o.getVideoUrl().split('&')[0]; // remove any extra parameters - we just want the first one, which is the video ID.
}
this.videoTitle = function() {
// titles have to be defined in an external object
if( window['_ytmeta'] ) return window['_ytmeta'][ this.id ].title || '';
}
}
Hopefully, someone in the future will find this helpful, because it was a serious pain in the ass to get it working!
Thank you everyone who posted their ideas here. :)