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jQuery plugin template - best practice, convention, performance and memory impact - javascript

I've started to write few jQuery plugins and figured it'd be nice to setup my IDE with a jQuery plugin template.
I have been reading some articles and posts on this site related to plugin convention, design, etc.. and thought I'd try and consolidate all of that.
Below is my template, I am looking to use it frequently so was keen to ensure it generally conforms to jQuery plugin design convention and whether the idea of having multiple internal methods (or even its general design) would impact performance and be prone to memory issues.
(function($)
{
var PLUGIN_NAME = "myPlugin"; // TODO: Plugin name goes here.
var DEFAULT_OPTIONS =
{
// TODO: Default options for plugin.
};
var pluginInstanceIdCount = 0;
var I = function(/*HTMLElement*/ element)
{
return new Internal(element);
};
var Internal = function(/*HTMLElement*/ element)
{
this.$elem = $(element);
this.elem = element;
this.data = this.getData();
// Shorthand accessors to data entries:
this.id = this.data.id;
this.options = this.data.options;
};
/**
* Initialises the plugin.
*/
Internal.prototype.init = function(/*Object*/ customOptions)
{
var data = this.getData();
if (!data.initialised)
{
data.initialised = true;
data.options = $.extend(DEFAULT_OPTIONS, customOptions);
// TODO: Set default data plugin variables.
// TODO: Call custom internal methods to intialise your plugin.
}
};
/**
* Returns the data for relevant for this plugin
* while also setting the ID for this plugin instance
* if this is a new instance.
*/
Internal.prototype.getData = function()
{
if (!this.$elem.data(PLUGIN_NAME))
{
this.$elem.data(PLUGIN_NAME, {
id : pluginInstanceIdCount++,
initialised : false
});
}
return this.$elem.data(PLUGIN_NAME);
};
// TODO: Add additional internal methods here, e.g. Internal.prototype.<myPrivMethod> = function(){...}
/**
* Returns the event namespace for this widget.
* The returned namespace is unique for this widget
* since it could bind listeners to other elements
* on the page or the window.
*/
Internal.prototype.getEventNs = function(/*boolean*/ includeDot)
{
return (includeDot !== false ? "." : "") + PLUGIN_NAME + "_" + this.id;
};
/**
* Removes all event listeners, data and
* HTML elements automatically created.
*/
Internal.prototype.destroy = function()
{
this.$elem.unbind(this.getEventNs());
this.$elem.removeData(PLUGIN_NAME);
// TODO: Unbind listeners attached to other elements of the page and window.
};
var publicMethods =
{
init : function(/*Object*/ customOptions)
{
return this.each(function()
{
I(this).init(customOptions);
});
},
destroy : function()
{
return this.each(function()
{
I(this).destroy();
});
}
// TODO: Add additional public methods here.
};
$.fn[PLUGIN_NAME] = function(/*String|Object*/ methodOrOptions)
{
if (!methodOrOptions || typeof methodOrOptions == "object")
{
return publicMethods.init.call(this, methodOrOptions);
}
else if (publicMethods[methodOrOptions])
{
var args = Array.prototype.slice.call(arguments, 1);
return publicMethods[methodOrOptions].apply(this, args);
}
else
{
$.error("Method '" + methodOrOptions + "' doesn't exist for " + PLUGIN_NAME + " plugin");
}
};
})(jQuery);
Thanks in advance.

A while back I've build a plugin generator based on a blog article I have read: http://jsfiddle.net/KeesCBakker/QkPBF/. It might be of use. It is fairly basic and straight forward. Any comments would be very welcome.
You can fork your own generator and change it to your needs.
Ps. This is the generated body:
(function($){
//My description
function MyPluginClassName(el, options) {
//Defaults:
this.defaults = {
defaultStringSetting: 'Hello World',
defaultIntSetting: 1
};
//Extending options:
this.opts = $.extend({}, this.defaults, options);
//Privates:
this.$el = $(el);
}
// Separate functionality from object creation
MyPluginClassName.prototype = {
init: function() {
var _this = this;
},
//My method description
myMethod: function() {
var _this = this;
}
};
// The actual plugin
$.fn.myPluginClassName = function(options) {
if(this.length) {
this.each(function() {
var rev = new MyPluginClassName(this, options);
rev.init();
$(this).data('myPluginClassName', rev);
});
}
};
})(jQuery);

[Edit] 7 months later
Quoting from the github project
jQuery is no good, and jQuery plugins is not how do modular code.
Seriously "jQuery plugins" are not a sound architecture strategy. Writing code with a hard dependency on jQuery is also silly.
[Original]
Since I gave critique about this template I will propose an alternative.
To make live easier this relies on jQuery 1.6+ and ES5 (use the ES5 Shim).
I've spend some time re-designing the plugin template you've given and rolled out my own.
Links:
Github
Documentation
Unit tests Confirmed to pass in FF4, Chrome and IE9 (IE8 & OP11 dies. known bug).
Annotated Source Code
The PlaceKitten example plugin
Comparison:
I've refactored the template so that it's split into boilerplate (85%) and scaffolding code (15%). The intention is that you only have to edit the scaffolding code and you can keep leave boilerplate code untouched. To achieve this I've used
inheritance var self = Object.create(Base) Rather then editing the Internal class you have directly you should be editing a sub class. All your template / default functionality should be in a base class (called Base in my code).
convention self[PLUGIN_NAME] = main; By convention the plugin defined on jQuery will call the method define on self[PLUGIN_NAME] by default. This is considered the main plugin method and has a seperate external method for clarity.
monkey patching $.fn.bind = function _bind ... Use of monkey patching means that the event namespacing is done automatically for you under the hood. This functionality is free and does not come at the cost of readability (calling getEventNS all the time).
OO Techniques
It's better to stick to proper JavaScript OO rather then classical OO emulation. To achieve this you should use Object.create. (which ES5 just use the shim to upgrade old browsers).
var Base = (function _Base() {
var self = Object.create({});
/* ... */
return self;
})();
var Wrap = (function _Wrap() {
var self = Object.create(Base);
/* ... */
return self;
})();
var w = Object.create(Wrap);
This is different from the standard new and .prototype based OO people are used to. This approach is preferred because it re-inforces the concept that there are only Objects in JavaScript and it's a prototypical OO approach.
[getEventNs]
As mentioned this method has been refactored away by overriding .bind and .unbind to automatically inject namespaces. These methods are overwritten on the private version of jQuery $.sub(). The overwritten methods behave the same way as your namespacing does. It namespaces events uniquely based on plugin and instance of a plugin wrapper around a HTMLElement (Using .ns.
[getData]
This method has been replaced with a .data method that has the same API as jQuery.fn.data. The fact that it's the same API makes it easier to use, its basically a thin wrapper around jQuery.fn.data with namespacing. This allows you to set key/value pair data that is immediatley stored for that plugin only. Multiple plugins can use this method in parallel without any conflicts.
[publicMethods]
The publicMethods object has been replaced by any method being defined on Wrap being automatically public. You can call any method on a Wrapped object directly but you do not actually have access to the wrapped object.
[$.fn[PLUGIN_NAME]]
This has been refactored so it exposes a more standardized API. This api is
$(selector).PLUGIN_NAME("methodName", {/* object hash */}); // OR
$(selector).PLUGIN_NAME({/* object hash */}); // methodName defaults to PLUGIN_NAME
the elements in the selector are automatically wrapped in the Wrap object, the method is called or each selected element from the selector and the return value is always a $.Deferred element.
This standardizes the API and the return type. You can then call .then on the returned deferred to get out the actual data you care about. The use of deferred here is very powerful for abstraction away whether the plugin is synchronous or asynchronous.
_create
A caching create function has been added. This is called to turn a HTMLElement into a Wrapped element and each HTMLElement will only be wrapped once. This caching gives you a solid reduction in memory.
$.PLUGIN_NAME
Added another public method for the plugin (A total of two!).
$.PLUGIN_NAME(elem, "methodName", {/* options */});
$.PLUGIN_NAME([elem, elem2, ...], "methodName", {/* options */});
$.PLUGIN_NAME("methodName", {
elem: elem, /* [elem, elem2, ...] */
cb: function() { /* success callback */ }
/* further options */
});
All parameters are optional. elem defaults to <body>, "methodName" defaults to "PLUGIN_NAME" and {/* options */} defaults to {}.
This API is very flexible (with 14 method overloads!) and standard enough to get used to the syntnax for every method your plugin will expose.
Public exposure
The Wrap, create and $ objects are exposed globally. This will allow advanced plugin users maximum flexibility with your plugin. They can use create and the modified subbed $ in their development and they can also monkey patch Wrap. This allows for i.e. hooking into your plugin methods. All three of these are marked with a _ in front of their name so they are internal and using them breaks the garantuee that your plugin works.
The internal defaults object is also exposed as $.PLUGIN_NAME.global. This allows users to override your defaults and set plugin global defaults. In this plugin setup all hashes past into methods as objects are merged with the defaults, so this allows users to set global defaults for all your methods.
Actual Code
(function($, jQuery, window, document, undefined) {
var PLUGIN_NAME = "Identity";
// default options hash.
var defaults = {
// TODO: Add defaults
};
// -------------------------------
// -------- BOILERPLATE ----------
// -------------------------------
var toString = Object.prototype.toString,
// uid for elements
uuid = 0,
Wrap, Base, create, main;
(function _boilerplate() {
// over-ride bind so it uses a namespace by default
// namespace is PLUGIN_NAME_<uid>
$.fn.bind = function _bind(type, data, fn, nsKey) {
if (typeof type === "object") {
for (var key in type) {
nsKey = key + this.data(PLUGIN_NAME)._ns;
this.bind(nsKey, data, type[key], fn);
}
return this;
}
nsKey = type + this.data(PLUGIN_NAME)._ns;
return jQuery.fn.bind.call(this, nsKey, data, fn);
};
// override unbind so it uses a namespace by default.
// add new override. .unbind() with 0 arguments unbinds all methods
// for that element for this plugin. i.e. calls .unbind(_ns)
$.fn.unbind = function _unbind(type, fn, nsKey) {
// Handle object literals
if ( typeof type === "object" && !type.preventDefault ) {
for ( var key in type ) {
nsKey = key + this.data(PLUGIN_NAME)._ns;
this.unbind(nsKey, type[key]);
}
} else if (arguments.length === 0) {
return jQuery.fn.unbind.call(this, this.data(PLUGIN_NAME)._ns);
} else {
nsKey = type + this.data(PLUGIN_NAME)._ns;
return jQuery.fn.unbind.call(this, nsKey, fn);
}
return this;
};
// Creates a new Wrapped element. This is cached. One wrapped element
// per HTMLElement. Uses data-PLUGIN_NAME-cache as key and
// creates one if not exists.
create = (function _cache_create() {
function _factory(elem) {
return Object.create(Wrap, {
"elem": {value: elem},
"$elem": {value: $(elem)},
"uid": {value: ++uuid}
});
}
var uid = 0;
var cache = {};
return function _cache(elem) {
var key = "";
for (var k in cache) {
if (cache[k].elem == elem) {
key = k;
break;
}
}
if (key === "") {
cache[PLUGIN_NAME + "_" + ++uid] = _factory(elem);
key = PLUGIN_NAME + "_" + uid;
}
return cache[key]._init();
};
}());
// Base object which every Wrap inherits from
Base = (function _Base() {
var self = Object.create({});
// destroy method. unbinds, removes data
self.destroy = function _destroy() {
if (this._alive) {
this.$elem.unbind();
this.$elem.removeData(PLUGIN_NAME);
this._alive = false;
}
};
// initializes the namespace and stores it on the elem.
self._init = function _init() {
if (!this._alive) {
this._ns = "." + PLUGIN_NAME + "_" + this.uid;
this.data("_ns", this._ns);
this._alive = true;
}
return this;
};
// returns data thats stored on the elem under the plugin.
self.data = function _data(name, value) {
var $elem = this.$elem, data;
if (name === undefined) {
return $elem.data(PLUGIN_NAME);
} else if (typeof name === "object") {
data = $elem.data(PLUGIN_NAME) || {};
for (var k in name) {
data[k] = name[k];
}
$elem.data(PLUGIN_NAME, data);
} else if (arguments.length === 1) {
return ($elem.data(PLUGIN_NAME) || {})[name];
} else {
data = $elem.data(PLUGIN_NAME) || {};
data[name] = value;
$elem.data(PLUGIN_NAME, data);
}
};
return self;
})();
// Call methods directly. $.PLUGIN_NAME(elem, "method", option_hash)
var methods = jQuery[PLUGIN_NAME] = function _methods(elem, op, hash) {
if (typeof elem === "string") {
hash = op || {};
op = elem;
elem = hash.elem;
} else if ((elem && elem.nodeType) || Array.isArray(elem)) {
if (typeof op !== "string") {
hash = op;
op = null;
}
} else {
hash = elem || {};
elem = hash.elem;
}
hash = hash || {}
op = op || PLUGIN_NAME;
elem = elem || document.body;
if (Array.isArray(elem)) {
var defs = elem.map(function(val) {
return create(val)[op](hash);
});
} else {
var defs = [create(elem)[op](hash)];
}
return $.when.apply($, defs).then(hash.cb);
};
// expose publicly.
Object.defineProperties(methods, {
"_Wrap": {
"get": function() { return Wrap; },
"set": function(v) { Wrap = v; }
},
"_create":{
value: create
},
"_$": {
value: $
},
"global": {
"get": function() { return defaults; },
"set": function(v) { defaults = v; }
}
});
// main plugin. $(selector).PLUGIN_NAME("method", option_hash)
jQuery.fn[PLUGIN_NAME] = function _main(op, hash) {
if (typeof op === "object" || !op) {
hash = op;
op = null;
}
op = op || PLUGIN_NAME;
hash = hash || {};
// map the elements to deferreds.
var defs = this.map(function _map() {
return create(this)[op](hash);
}).toArray();
// call the cb when were done and return the deffered.
return $.when.apply($, defs).then(hash.cb);
};
}());
// -------------------------------
// --------- YOUR CODE -----------
// -------------------------------
main = function _main(options) {
this.options = options = $.extend(true, defaults, options);
var def = $.Deferred();
// Identity returns this & the $elem.
// TODO: Replace with custom logic
def.resolve([this, this.elem]);
return def;
}
Wrap = (function() {
var self = Object.create(Base);
var $destroy = self.destroy;
self.destroy = function _destroy() {
delete this.options;
// custom destruction logic
// remove elements and other events / data not stored on .$elem
$destroy.apply(this, arguments);
};
// set the main PLUGIN_NAME method to be main.
self[PLUGIN_NAME] = main;
// TODO: Add custom logic for public methods
return self;
}());
})(jQuery.sub(), jQuery, this, document);
As can be seen the code your supposed to edit is below the YOUR CODE line. The Wrap object acts similarly to your Internal object.
The function main is the main function called with $.PLUGIN_NAME() or $(selector).PLUGIN_NAME() and should contain your main logic.

How about something like this ? It's much clearer but again it would be nice to hear from you if you can improve it without overcomplicating its simplicity.
// jQuery plugin Template
(function($){
$.myPlugin = function(options) { //or use "$.fn.myPlugin" or "$.myPlugin" to call it globaly directly from $.myPlugin();
var defaults = {
target: ".box",
buttons: "li a"
};
options = $.extend(defaults, options);
function logic(){
// ... code goes here
}
//DEFINE WHEN TO RUN THIS PLUGIN
$(window).on('load resize', function () { // Load and resize as example ... use whatever you like
logic();
});
// RETURN OBJECT FOR CHAINING
// return this;
// OR FOR FOR MULTIPLE OBJECTS
// return this.each(function() {
// // Your code ...
// });
};
})(jQuery);
// USE EXAMPLE with default settings
$.myPlugin(); // or run plugin with default settings like so.
// USE EXAMPLE with overwriten settings
var options = {
target: "div.box", // define custom options
buttons: ".something li a" // define custom options
}
$.myPlugin(options); //or run plugin with overwriten default settings

I've been googling and landed here so, I have to post some ideas: first I agree with #Raynos.
The most code out there that tries to build a jQuery plugin actually...is not a plugin! It's just an object stored in memory which is refered by the data property of a node/element. That's because jQuery should be seen and used as a tool side by side with a class library (to remedy js inconsistencies from OO architecture) to build better code and yes this is not bad at all!
If you don't like classical OO behaviour stick to a prototypal library like clone.
So what our options really?
use JQueryUI/Widget or a similar library that hides technicalities and
provides abstraction
don't use them because of complexities, learning curve and god knows future changes
don't use them becuase you want to insist on modular design, build small-increase later
don't use them because you might want porting/connecting your code with different libraries.
Suppose the issues addressed by the following scenario (see the complexities from this question: Which jQuery plugin design pattern should I use?):
we have nodes A, B and C that store an object reference into their data property
some of them store info in public and private accessible internal objects,
some classes of these objects are connected with inheritance,
all of these nodes also need some private and public singletons to work best.
What would we do? See the drawning:
classes : | A B C
------------------case 1----------
members | | | |
of | v v v
an object | var a=new A, b=new B, c=new C
at | B extends A
node X : | a, b, c : private
------------------case 2---------
members | | | |
of | v v v
an object | var aa=new A, bb=new B, cc=new C
at | BB extends AA
node Y : | aa, bb, cc : public
-------------------case 3--------
members | | | |
of | v v v
an object | var d= D.getInstance() (private),
at | e= E.getInstance() (public)
node Z : | D, E : Singletons
as you can see every node refers to an object - a jQuery approach - but these objects change wildely; they contain object-properties with different data stored in or, even singletons that should be...single in memory like the prototype functions of the objects. We don't want every object's function belonging to class A to be repeatedly duplicated in memory in every node's object!
Before my answer see a common approach I've seen in jQuery plugins - some of them very popular but I don't say names:
(function($, window, document, undefined){
var x = '...', y = '...', z = '...',
container, $container, options;
var myPlugin = (function(){ //<----the game is lost!
var defaults = {
};
function init(elem, options) {
container = elem;
$container = $(elem);
options = $.extend({}, defaults, options);
}
return {
pluginName: 'superPlugin',
init: function(elem, options) {
init(elem, options);
}
};
})();
//extend jquery
$.fn.superPlugin = function(options) {
return this.each(function() {
var obj = Object.create(myPlugin); //<---lose, lose, lose!
obj.init(this, options);
$(this).data(obj.pluginName, obj);
});
};
}(jQuery, window, document));
I was watching some slides at: http://www.slideshare.net/benalman/jquery-plugin-creation from Ben Alman where he refers at slide 13 to object literals as singletons and that just knock me over: this is what the above plugin does, it creates one singleton with no chance whatsover to alter it's internal state!!!
Furthermore, at the jQuery part it stores a common reference to every single node!
My solution uses a factory to keep internal state and return an object plus it can be expanded with a class library and split in different files:
;(function($, window, document, undefined){
var myPluginFactory = function(elem, options){
........
var modelState = {
options: null //collects data from user + default
};
........
function modeler(elem){
modelState.options.a = new $$.A(elem.href);
modelState.options.b = $$.B.getInstance();
};
........
return {
pluginName: 'myPlugin',
init: function(elem, options) {
init(elem, options);
},
get_a: function(){return modelState.options.a.href;},
get_b: function(){return modelState.options.b.toString();}
};
};
//extend jquery
$.fn.myPlugin = function(options) {
return this.each(function() {
var plugin = myPluginFactory(this, options);
$(this).data(plugin.pluginName, plugin);
});
};
}(jQuery, window, document));
My project: https://github.com/centurianii/jsplugin
See: http://jsfiddle.net/centurianii/s4J2H/1/

Related

This is a strange one, but I'm exploring it to see if it's possible.
Let's say that I have a .NET application where I am using PubSub. I want a way to define the topic string using chained objects (not functions). The goal is to allow me a way of defining strings that lets me to take advantage of Visual Studio's IntelliSense and reduce the likelihood of spelling errors.
Here's an example:
/* Manual way */
var topic = "App.Navigation.CurrentItem"
/* Desired Solution */
// ... define the objects here ...
var topic = App.Navigation.CurrentItem;
console.log(topic); // "App.Navigation.CurrentItem"
var topic2 = App.Footer.CurrentItem;
console.log(topic2); // "App.Footer.CurrentItem"
I'd like each object to be responsible for outputing it's own value, and have the chaining process responsible for joining itself to the previous chained object via a predefined separator (in my case, a period [.]).
I've been playing with JavaScript getter syntax, but I'm curious if there's a better way.
Has anyone done something like this before, and if so, how did you solve it?

You're requirements aren't totally clear to me, but are you looking for something like this?
function namespace(ns) { this._ns = ns; }
namespace.prototype.toString = function() {return this._ns};
namespace.prototype.extend = function(suffix) {
return new namespace(this._ns + "." + suffix)
};
Usage:
App = new namespace('App');
App.Navigation = App.extend('Navigation');
App.Navigation.CurrentItem = App.Navigation.extend('CurrentItem');
console.log(App.Navigation.CurrentItem.toString()); // "App.Navigation.CurrentItem"

This is what I ended up with after reviewing StriplingWarrior's answer:
function Namespace(name, config) {
if (typeof name === "object") {
config = name;
name = null;
}
config = config || {};
this._ns = name;
this.define(config);
}
Namespace.prototype.toString = function() { return this._ns };
Namespace.prototype.define = function(config, base) {
base = base || this;
for (key in config) {
var name = (base._ns) ? base._ns + "." + key : key;
base[key] = new Namespace(name);
base.define(config[key], base[key]);
}
return base;
};
Usage:
var App = new Namespace("App", {
Navigation: {
Items: {
Current: {}
}
},
Content: {},
Footer: {
Items: {
Current: {}
}
}
});
console.log(App.toString()); // App
console.log(App.Navigation.Items.Current.toString()); // App.Navigation.Items.Current
console.log(App.Footer.toString()); // App.Footer
I also wrote a convenience method to reduce the toString():
function NS(namespace) {
return namespace.toString();
}
console.log(NS(App.Navigation.Items.Current));
Thanks again to StriplingWarrior for the the help!

I need to extend a jQuery Plugin (https://github.com/idiot/unslider) in order to add additional behavior with another public method.
(function(){
// Store a reference to the original remove method.
var originalMethod = $.fn.unslider;
// Define overriding method.
$.fn.unslider = function(){
// Execute the original method.
originalMethod.apply( this, arguments );
console.log( "Override method" );
function test() {
console.log("test called");
}
this.each(function() {
// Operations for each DOM element
console.log("each dom element?");
}).data('unslider', {
// Make test accessible from data instance
test: test
});
return this;
}
})(jQuery);
I already managed to make the public method accessible when calling
var slider = $('#slider');
slider.data('unslider').test();
However, I want to keep the old behavior of unslider anyways, but extend the Plugin with another function. Does anyone have an idea?
I created a fiddle, so you can check whats happening:
My new function gets called, but the old ones are gone:
http://jsfiddle.net/b2os4s7e/1/

If you look at the source of unslider, you can see it stores the Unslider instance inside the data:
// Enable multiple-slider support
return this.each(function(index) {
// Cache a copy of $(this), so it
var me = $(this),
key = 'unslider' + (len > 1 ? '-' + ++index : ''),
instance = (new Unslider).init(me, o);
// Invoke an Unslider instance
me.data(key, instance).data('key', key);
});
In your code you're overwriting this object with your own object. However, the slider expects there to be an Unslider instance. So what you want to do is get this instance and then extend it with your own functions:
var key = $(this).data('key');
var obj = $(this).data(key);
obj.test = function() { console.log('Working!'); };
See http://jsfiddle.net/b2os4s7e/2/

Just define:
$fn.unslider2 = function() { ... }
With any name and behaviour you like.

For extend JQuery should use .fn.extend
(function($){
$.fn.extend({
helloworld: function(message){
return this.each(function(){
$(this).click(function(){
alert(message);
});
});
}
});
})(jQuery)
the object .fn.extend is used for extend funcionality of jQuery

Thanks for your answers! I did it this way:
(function($){
var originalMethod = $.fn.unslider;
$.fn.extend({
unslider: function(o) {
var len = this.length;
var applyMethod = originalMethod.apply( this, arguments );
var key = applyMethod.data('key');
var instance = applyMethod.data(key);
// Cache a copy of $(this), so it
var me = $(this);
if (instance) {
instance.movenext = function (callback) {
return instance.stop().to(instance.i + 1, callback);
};
instance.moveprev = function (callback) {
return instance.stop().to(instance.i - 1, callback);
};
}
return applyMethod.data(key, instance);
}
});
})(jQuery)
The key was to address the data attribute as sroes suggested.
Moreover i needed to apply the original method, since i need the old methods.

I want to enforce a miterLimit in actual pixels rather than as a ratio of the lineWidth. To do this, I'd like to hook any changes to lineWidth, and set the miterLimit simultaneously and automatically. I've used custom setters on objects before, but if I replace the lineWidth setter, I don't know of any way to actually pass the value to set on through to the actual canvas context.
Is there some way (compatible on IE9+) that I can listen to changes to a given key on an object without changing the behavior of setting that value?

Your getter/setter idea is a good one...
How about just adding a property definition to your context object?
Add a myLineWidth property to your context object and then set the linewidth using context.myLineWidth instead of context.lineWidth.
Some example code:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
Object.defineProperty(ctx, 'myLineWidth', {
get: function() {
return(this.lineWidth);
},
set: function(newWidth) {
this.lineWidth=newWidth;
console.log("Executed myLineWidth setter: ",this.lineWidth);
}
});
ctx.myLineWidth=5;
ctx.strokeRect(100,100,50,50);
Alternate Method using Encapsulation:
JavaScript does have true inheritance so it's not possible to inherit & override lineWidth.
The next best thing would be encapsulating the context object. Then all coders can use the encapsulated version of the context using the standard property and method syntax (no need for myLineWidth). If needed, here's a how-to: http://aboutcode.net/2011/10/04/efficient-encapsulation-of-javascript-objects.html.
I did a similar encapsulation in order to log the context drawings. Below, I've tried to snip the encapsulation code from one of my projects. You can ignore my special handling of drawImage and gradients as I needed to grab values from these that you won't need to grab--just add those methods to the returnMethods[] array.
Some example code for you to start with:
// Log all context drawings
// Creates a proxy class wrapping canvas context
function LoggedContext(canvas,context) {
var self = this;
this.canvas=canvas;
this.context=context;
this.imageURLs=[];
this.log=[];
this.gradients=[];
this.patterns=[];
this.init(self);
}
// maintain urls of images used
LoggedContext.prototype.imageIndex=function(url){
var i=a.indexOf(url);
// found
if(i>-1){ return(i); }
// not found -- added
a.push(url);
return(a.length-1);
}
///////////////////////////////////////////
// These methods require special handling
// (drawImage:need image.src, gradients:need gradDefs & colors)
//
LoggedContext.prototype.drawImage=function(){
this.context.drawImage.apply(this.context,arguments);
var args = Array.prototype.slice.call(arguments);
args[0]=arguments[0].src;
args.unshift(2,"drawImage");
var sArgs=JSON.stringify(args);
this.log.push(sArgs);
return(this);
}
//
LoggedContext.prototype.createLinearGradient =function(x1,y1,x2,y2){
var gradient=this.context.createLinearGradient(x1,y1,x2,y2);
gradient.context=this;
gradient.gradientID=this.gradients.length;
this.gradients.push({line:{x1:x1,y1:y1,x2:x2,y2:y2},stops:[]});
gradient.baseAddColorStop=gradient.addColorStop;
gradient.addColorStop=function(stop,color){
this.context.gradients[this.gradientID].stops.push({stop:stop,color:color});
this.baseAddColorStop(stop,color);
}
return(gradient);
}
//
LoggedContext.prototype.createPattern =function(i,r){
var pattern=this.context.createPattern(i,r);
pattern.patternID=this.patterns.length;
this.patterns.push({src:i.src,repeat:r});
return(pattern);
}
//
LoggedContext.prototype.createRadialGradient =function(sx,sy,sr,ex,ey,er){
var gradient=this.context.createRadialGradient(sx,sy,sr,ex,ey,er);
gradient.context=this;
gradient.gradientID=this.gradients.length;
this.gradients.push({circles:{sx:sx,sy:sy,sr:sr,ex:ex,ey:ey,er:er},stops:[]});
gradient.baseAddColorStop=gradient.addColorStop;
gradient.addColorStop=function(stop,color){
this.context.gradients[this.gradientID].stops.push({stop:stop,color:color});
this.baseAddColorStop(stop,color);
}
return(gradient);
}
// load the proxy object with all properties & methods of the context
LoggedContext.prototype.init=function(self){
// define public context properties
var properties={
//
fillStyle:"black",
strokeStyle:"black",
lineWidth:1,
font:"10px sans-serif",
//
globalAlpha:1.00,
globalCompositeOperation:"source-over",
//
shadowColor:"black",
shadowBlur:0,
shadowOffsetX:0,
shadowOffsetY:0,
//
lineCap:"butt", // butt,round,square
lineJoin:"miter", // miter,round,miter
miterLimit:10,
//
textAlign:"start",
textBaseLine:"alphabetic",
};
// encapsulate public properties
for (var i in properties) {
(function(i) {
if(!(i=="fillStyle")){
Object.defineProperty(self, i, {
get: function () {
return properties[i];
},
set: function (val) {
this.log.push(JSON.stringify([1,i,val]));
properties[i] = val;
this.context[i]=val;
}
})
}else{
Object.defineProperty(self, i, {
get: function () {
return properties[i];
},
set: function (val) {
if(typeof val ==="object"){
if(val.gradientID>=0){
this.log.push(JSON.stringify([1,i,"gradient",val.gradientID]));
}else if(val.patternID>=0){
this.log.push(JSON.stringify([1,i,"pattern",val.patternID]));
}
}else{
this.log.push(JSON.stringify([1,i,val]));
}
properties[i] = val;
this.context[i]=val;
}
})
}
})(i);
}
// define public context methods
var methods = ['arc','beginPath','bezierCurveTo','clearRect','clip',
'closePath','fill','fillRect','fillText','lineTo','moveTo',
'quadraticCurveTo','rect','restore','rotate','save','scale','setTransform',
'stroke','strokeRect','strokeText','transform','translate','putImageData'];
// encapsulate public methods
for (var i=0;i<methods.length;i++){
var m = methods[i];
this[m] = (function(m){
return function () {
this.context[m].apply(this.context, arguments);
// "arguments" is not a real array--so convert it
var args = Array.prototype.slice.call(arguments);
args.unshift(2,m);
var sArgs=JSON.stringify(args);
this.log.push(sArgs);
return(this);
};}(m));
}
// define context methods that return values
var returnMethods = ['measureText','getImageData','toDataURL',
'isPointInPath','isPointInStroke'];
// encapsulate return methods
for (var i=0;i<returnMethods.length;i++){
var m = returnMethods[i];
this[m] = (function(m){
return function () {
return(this.context[m].apply(this.context, arguments));
};}(m));
}
} // end init()

is there a way to define global namespace, so that i can call function from this namespace from all my page?
e.g
// in one file i define below code
DefineNameSpace("my.namespace.api", {
addObject: function(obj) {
// store obj into indexDB
},
readAllObject: function() {
// return array of object from indexdb
}
})
// so that in another javascript file i can do
my.namespace.api.addObject({name: "foo", desc: "bar"});
is there a way to implement "DefineNameSpace" method?
Thanks

one way to do it, which is very simple, is this:
my = {
namespace: {
api : {}
}
}
my.namespace.api.addObject = function (obj) { }
you're actually creating objects but in this way it will function as a namespace just as well :)
hm it's not the method you're implementing. But building a namespace with a method would require the function to be called before the script files are loaded where the namespace is used like that, otherwise those lines of code are called before the DefineNamespace method is called and you will run into parts of namespaces that are undefined at that point. With above solution that won't be the case, although it is not dynamic unfortunately.

building a namespace dynamically can be done in the following way:
// the root of the namespace would still be handy to have declared here
var my = {};
function defineNamespace(namespaceStr) {
var namespaceSegments = namespaceStr.split(".");
var namespaceSoFar = null;
// iterate through namespace parts
for (var i = 0; i < namespaceSegments.length; i++) {
var segment = namespaceSegments[i];
if (i == 0) {
// if namespace starts with my, use that
if (segment == "my") {
// set pointer to my
namespaceSoFar = my;
}
else {
// create new root namespace (not tested this, but think this should work)
var otherNamespace = eval(segment);
if (typeof otherNamespace == "undefined") {
eval(segment + " = {};");
}
// set pointer to created root namespace
namespaceSoFar = eval(segment);
}
}
else {
// further build the namespace
if (typeof namespaceSoFar[segment] == "undefined") {
namespaceSoFar[segment] = {};
}
// update the pointer (my -> my.namespace) for use in the next iteration
namespaceSoFar = namespaceSoFar[segment];
}
}
}

Given these snippets (hopefully complete enough for this question)...
ModelA.js (has many modelBs):
ModelBs = (function(_super) {
ModelB.prototype.bWithName = function(name) {
return this.find(function (b) {
return b.name == name;
});
}
})(Backbone.Collection);
return ModelA = (function(_super) {
...
ModelA.prototype.initialize = function() {
this.modelbs = new ModelBs(this.modelbs, {});
};
ModelA.prototype.bWithName = function(name) {
return this.modelbs.bWithName(name);
};
return modelA;
})(BaseModel);
ModelC.js (has one modelA):
ModelC.prototype.toString = function(opts) {
...
console.log(this.modelA); // defined...
console.log(this.modelA.modelBs); // defined...
console.log(this.modelA.bWithName("foo")); // undefined
...
}
In ModelC.js, why are this.modelA and this.modelA.modelBs defined, but this.modelA.bWithName() undefined, and how can I fix it?
This works: this.modelA.modelBs.first().
This returns undefined: this.modelA.modelBs.where({name:"foo"}).
In the web console, this works: modelZ.modelAs.first().bWithName("foo").attributes.
Are accessors or methods in general not available through other models?
Thanks-

Bah. The method was in fact available, but the strict equals (===) was killing the search. In one instance I was trying to search with the wrong typeof name.
Thanks for the input though!