Develop Reference

Is WeakMap performance influenced by the Key Object?

When using a WeakMap Object in JavaScript, the get and set methods require a Key to be passed in as argument.
FYI, I'm using WeakMap to simulate private properties for a class, something like this:
window.MyObject = (function(){
let _privateProperty = new WeakMap();
class MyObject {
constructor(value) {
_privateVariable.set(this, value);
}
SamplePrivateGet() {
return _privateVariable.get(this);
}
}
return MyObject;
})();
My question is: is get and set performance influenced by the object used as key?
I know primitive types can't be used as key, but maybe using an object with only one property as key could be faster than using an object that has, say, one thousand properties.
I tried looking at ECMA specifications but it's not specified, my guess is it's because it would depends on the browser's implementation.
EDIT: There are two ways to approach this with WeakMaps, one is declaring a single _privateProperties WeakMap to which I will add my private properties, the other declare one WeakMap for each of the private properties. I'm currently using the second approach so that every WeakMap can be Garbage Collected separately, but maybe going with the first would allow me to make much less .get calls. But I guess that's out of the scope of the question :)

Not sure if this is good idea, but you could make kind of private instance properties by using Symbols.
const PRIVATE_VAR = Symbol('MY_CLASS::PRIVATE_VAR');
const PRIVATE_FUNC = Symbol('MY_CLASS::PRIVATE_FUNC');
export default class MyClass{
constructor(value){
this[PRIVATE_VAR] = value;
}
[PRIVATE_FUNC](){
/* ... */
}
}
Without access to those Symbols values, it is quite hard to access those specific instance properties (plus instance properties defined with Symbols are non-enumerable in classes and objects).
btw 'Private instance methods and accessors' are at stage 3 so such solutions might not be relevant soon
https://github.com/tc39/proposals

Alternative methods for extending object.prototype when using jQuery

Some time ago I tried to extend Object.prototype... I was surprised when later I saw errors in the console which comes from jQuery file. I tried to figured out what is wrong and of course I found information that extending Object.prototype is a "evil", "you shouldn't do that because JS is dynamic language and your code will not work soon" and information that jQuery will now add hasOwnProperty method to their for in loops.
Because I didn't want to leave jQuery, I drop the idea about extending Object.prototype.
Till now. My project getting bigger and I am really annoyed because I have to repeat many times some parts of the code. Below is a bit of the structure which I am using in my projects:
charts.js:
CHARTS = {
_init: function () {
this.monthlyChart();
/*
*
* more propertys goes here
*
*/
return this;
},
monthlyChart: function () {
//create my chart
return {
update: function () {
// update chart
}
};
}()
/*
*
* more propertys goes here
*
*/
}._init;
dashboard.js
NAVBAR = {
_init: function () {
/*
*
* more propertys goes here
*
*/
return this;
},
doSomething: function(){
$(document).ready(function(){
$('.myButton').on('click', function(){
var data = [];
// calling property from charts.js
CHARTS.monthlyChart.update(data);
});
});
}
}._init
As I mentioned project is really big now - it's over 40 js files and some of them has a few thousands line of code. It is really annoying that I have to repeat _init section every time, as well as I many functions I have to repeat $(document).ready && $(window).load.
I tried to find another solution for my problem. I tried to create class with init property (more you can find here) but I this solution forced me to add another "unnecessary" piece of the code to every file and accessing other file object property makes it to complicated too (return proper objects everywhere etc). As advised in the comment I started reading about getters and setters in JS.
After all I created something like that:
//Auto initialization
if (typeof $document === 'undefined') {
var $document = $(document),
$window = $(window),
$body = $('body');
}
Object.defineProperty(Object.prototype, '_init', {
get: function () {
// if object has no property named `_init`
if (!this.hasOwnProperty('_init')) {
for (var key in this) {
// checking if name of property does starts from '_' and if it is function
if (this.hasOwnProperty(key) && key[0] === '_' && typeof this[key] === 'function') {
if (key.indexOf('_ready_') > -1) {
//add function to document ready if property name starts from '_ready_'
$document.ready(this[key].bind(this));
} else if (key.indexOf('_load_') > -1) {
//add function to window load if property name starts from '_load_'
$window.load(this[key].bind(this));
} else {
// else execute function now
this[key].bind(this)();
}
}
}
return this;
}
}
});
and my object:
var DASHBOARD = {
_runMe: function(){
},
_ready_runMeOnReady: function(){
},
_load_runMeOnLoad: function(){
},
iAmAString: ''
}._init
It seems that this solution works with jQuery. But is it safe to use? I don't see any problem the code can cause and I don't see any further problems that it may cause. I will be really happy if somebody will tell me why I shouldn't use this solution.
Also I'm trying to understand how it works in details. Theoretically I defined property for the Object.prototype by defineProperty, without assigning value to it. Somehow it doesn't cause any errors in jQuery fore in loop, why? Does that mean that property _init is not defined at some point or at all because I am defined only getter of it?
Any help will be appreciated :)

By not including the descriptor in Object.defineProperty(obj, prop, descriptor) JavaScript defaults all the Boolean descriptor attributes to false. Namely
writable, enumerable, and configurable. Your new property is hidden from the for in iterators because your _init property is enumerable:false.
I am not a fan of JQuery so will not comment on why in regard to JQuery
There is no absolute rule to adding properties to JavaScript's basic type and will depend on the environment that your code is running. Adding to the basic type will add it to the global namespace. If your application is sharing the namespace with 3rd party scripts you can potentially get conflicts, causing your code or the third party code or both to fail.
If you are the only code then conflicts will not be an issues, but adding to object.prototype will incur an addition overhead on all code that uses object.
I would strongly suggest that you re examine the need for a global _init. Surely you don't use it every time you need a new object. I am a fan of the add hock approach to JavaScript data structures and try to keep away from the formal OOP paradigms

Your question in fact contains two questions.
It seams that this solution works with jQuery. But is it safe to use? I don't see any problem the code can cause and I don't see any further problems that it may cause. I will be really happy if somebody will tell me why I shouldn't use this solution.
First of all, there are three main reasons to avoid modification of built-in prototypes.
For-in loops
There is too much code using for-in loop without hasOwnProperty check. In your case that is jQuery code that does not perform check.
Solutions
Don't use for-in loop without .hasOwnProperty check.
Doesn't apply in this case because it's third-party code and you can't modify it.
for-in loop traverses only enumerable keys.
You have used that solution. Object.defineProperty creates non-enumerable properties by default (ECMAScript 5.1 specification)
Not supported by IE8.
Conflicts
There is risk of property name. Imagine that you use jQuery plugin that checks for existence of ._init property on objects - and it can lead to subtle and hard to debug bugs. Names prefixed with underscore are widely used in modern JavaScript libraries for indicating private properties.
Encapsulation violation (bad design)
But you have worser problem. Definining global ._init property suggests that every object have universal initialization logic. It breaks encapsulation, because your objects don't have full control over their state.
You can't rely on presence of _init method due to this. Your coworkers can't implement their own class with
Alternative designs
Global initializer
You can create global function initialize and wrap all your objects that require initialization in it.
Decouple view and logic
Your objects should not merge logic and view in one object (it violates single responsibility principle) and you are victim of spaghetti code.
Moreover - object initialization should not bind it to DOM, some controller objects should be a proxy between your logic and display.
It can be good idea to inspect how popular client-side MVC frameworks have solved this problem (Angular, Ember, Backbone) have solved this problem.

Is it safe to use getters and setters?
Yes. But if you only support IE9+.
Is it safe to modify Object.prototype?
No. Create another object to inherit all of your application objects from.
Why extending basic JavaScript objects is eval evil?
Because EVERY SINGLE object created on the webpage where your script is loaded will inherit that property or method.
There is a lot cons like collisions and performance overhead if you do it that way.
There is a lot of ways to make it better, let me show you the one I use.
// Here we create the base object:
var someBaseObject = {};
someBaseObject.someMethod = function () {
// some code here
}
someBaseObject.someProperty = "something";
// And inherit another object from the someBaseObject
someObject = Object.create(someBaseObject);
someObject.someAnotherMethod = function () {
// some code here
}
This approach allow us to leave the Object prototype alone, and build a prototype chain where someObject inherits from someBaseObject, and someBaseObject inherits from Object.
The only thing I want to say by this post: leave base objects alone and build your own, so you will have much less headache.
Note: Object.create is supported in IE9+. Here is shim for IE8 and lower by Douglas Crockford:
if (typeof Object.create !== 'function') {
Object.create = function (o) {
function F() {}
F.prototype = o;
return new F();
};
}

Placing instance properties in prototype constructors, good or bad?

I just finished reading this very good article on prototypal inheritance in JavaScript, but was surprised to see how vehemently the author was against having properties defined in prototypes.
A common mistake when creating objects for the prototype chain, from programmers that come from classical OOP anyway, is to define common properties high up in the chain because they exist for all instances. We feel the need to define the property as if the abstract object described an interface. Yet there is no point in defining in a prototype a property that will be present in objects that descend from it. Javascript is not like Java : you don't declare in the base objects variables that will be different to all instances of the descendants. You declare a variable only on the level where it will be defined.
Take the name property of our animals. Since every animal has a name, it's natural to consider this property as common to all, and define it in the common denominator which is the Animal prototype. The thing is, Animal has no name. A Dog instance has a name.
In Javascript, you cannot say an Animal has a name. Animal is an object, not a definition, even if we use it like so. And that object has no name property. Why then is name referred to in Animal's methods if Animal has no name? Because Animal is abstract : it is not intended to be used by itself. this, in Animal, will never refer to Animal. It will refer to whatever object descends from Animal, dino for example. And dino has a name.
If I have a very complex set of classes that have, dozens of properties in common. I don't see how it's better to duplicate those properties and the work that goes into setting them up on each instantiable derived class when the work can be done once in the base class, even if that base class was meant to be 'abstract'.
For instance:
function Analysis(args){
args = args || {};
// Extract supported init properties from args
this.description = args.description;
this.host = args.host;
this.source = args.source;
this.identifier = args.identifier;
this.vendor = args.vendor;
this.agent = args.agent;
//etc...
}
function PortfolioAnalysis(args){
Analysis.call(this, args);
args = args || {};
this.portfolio = args.portfolio;
this.author = args.author;
//etc...
}
PortfolioAnalysis.prototype = Object.create(Analysis.prototype);
PortfolioAnalysis.prototype.constructor = PortfolioAnalysis;
function TreatyAnalysis(args){
Analysis.call(this, args);
args = args || {};
this.treaty = args.treaty;
this.terms = args.terms;
//etc...
}
TreatyAnalysis.prototype = Object.create(Analysis.prototype);
TreatyAnalysis.prototype.constructor = TreatyAnalysis;
//etc...
So the article is saying I should paste the initialization code for the properties description, host, source, etc. in each of the derived classes, and remove it from the base class.
I don't see why that's better, especially if there's a bunch of complex common logic around constructing these objects using those shared properties, what's so bad about defining them in the base class, and if it's so bad, is there a way around it that doesn't involve code duplication or having to define a separate '.init()' method?

So the article is saying I should paste the initialization code for the properties description, host, source, etc. in each of the derived classes, and remove it from the base class.
No. Your code is perfectly fine, exactly how it should be done.
And that article is saying that the properties like description, host etc should be placed on instances (like a new ThreatAnalysis(…), or even a new Analysis(…)), but not on Analysis.prototype - just what you are doing. There are some people who would "default", e.g. empty, identifiers etc on Analysis.prototype because they want to "declare" that every Analysis instance should have an identifier. That is rubbish, as the article explains.
To share your initialisation behaviour in the Analysis constructor is fine (as the article mentions, shared functions may be placed hight in the prototype chain). There's no need to inline it and make Analysis and empty object, even if it is abstract and will never be instantiated directly.

I don't think you get prototypal inheritance yet. The author is not saying “don't put the initialization code in the base constructor”. What the author is saying is “don't put properties on the base prototype”. It's totally different.
So you are allowed to do what you are currently doing. It's totally fine. What you shouldn't do however is put default values of properties on the prototype as it might cause problems. For example consider:
function Foo() {}
Foo.prototype.data = []; // you shouldn't do this
var a = new Foo;
var b = new Foo;
a.data.push(0);
alert(JSON.stringify(b.data)); // [0]
This is why you shouldn't share properties on the prototype. We modified the value of a.data but since data is shared amongst all instances of Foo we also modified b.data. Hence an invariant was violated.
Think about it like this:
The properties defined on the current object are its public properties. They are not shared.
The properties defined on the prototype of the current object are static properties. They are shared amongst the instances of the prototype.
Hence it's alright to define static properties, like the count of all the instances, on the prototype. However it's not alright to define public properties on the prototype because it may cause problems like the one above.
Dr. Alex Rauschmayer explains this better: http://www.2ality.com/2013/09/data-in-prototypes.html
Your code is fine because the this in your constructors always point to the current object, not the prototype. Hence you are not defining any properties on the prototype.
I think you got confused because of constructors vs prototypes. Perhaps this blog post would elucidate your doubts: http://aaditmshah.github.io/why-prototypal-inheritance-matters/

How to deal with and discern inheritance conflicts in JavaScript?

So the code below reflects the pseudo-classical version of inheritance in JavaScript.
function SynthOne() { // constructor 1
this.sound1 = "piano";
};
function SynthTwo() { // constructor 2
this.sound2 = "bass";
}
SynthOne.prototype = new SynthTwo; // overwrite constructor 1's prototype with constructor 2's
var synthsCombined = new SynthOne; // assign constructor 1 to variable
// this variable now has access to both constructors properties & methods
document.write(synthsCombined.sound1 + " ")
document.write(synthsCombined.sound2)
But let's change this to make sound1 and sound2 to simply sound.
Let's also assume that I really wanted to create an inheritance chain to access both of these "sounds" even if they were named the same thing. Is there a pattern in the JavaScript community or a coding convention that exist to deal with this kind of situation? Or am I just stuck?
Thank you

Child properties hide properties of the same name further up the prototype chain. Technically, you can still get access to the parent property like this:
Object.getPrototypeOf(synthsCombined).sound
Or the non-standard:
synthsCombined.__proto__.sound
But this probably isn't something you want to do. If you need both values, then name them different things.

it was simply something that entered my mind and I was curious about. I can see a situation where at the very least you combine constructors not realizing they have similar property/method names.
You hardly inherit from classes whose set of properties1 you do not know. If you subclass something, you often want to explicitly overwrite properties with more specific values - that's just what the shadowing is for.
In case you want to extend the set, you'd have to choose an unallocated name. In case of interface clashes (e.g. when extending the implementation), that's just a bug and either the base class or the child classes would need to change their identifier. Using descriptive names will lower the risk.
How to deal with this kind of situation?
If it's unwanted, fix the bug (this is not JavaScript-specific). If you deliberately have chosen the same property name, you can access the inherited value by manually ascending the prototype chain with Object.getPrototypeOf().
[1]: Speaking of both attributes and methods, as they're just properties in javascript

You could give one of your constructors a base property, which will get the properties from the inherited constructor:
function SynthOne() { // constructor 1
this.base = {};
this.sound = "piano";
SynthTwo.call(this.base);
};
function SynthTwo() { // constructor 2
this.sound = "bass";
}
SynthOne.prototype = Object.create(SynthTwo.prototype);
var synthsCombined = new SynthOne;
console.log(synthsCombined.sound); //piano
console.log(synthsCombined.base.sound); //bass
But from what it looks like you are trying to accomplish, maybe inheritance is not the right way for you. It might make more sense to create a generic Synth class and maybe a SynthCollection class, to combine different Synths.

Is John Resig's OO JavaScript implementation production safe?

For a long time I have been throwing around the idea of making my JavaScript more object oriented. I have looked at a few different implementations of this as well but I just cannot decide if it is necessary or not.
What I am trying to answer are the following questions
Is John Resig's simple inheritance structure safe to use for production?
Is there any way to be able to tell how well it has been tested?
Besides Joose what other choices do I have for this purpose? I need one that is easy to use, fast, and robust. It also needs to be compatible with jQuery.

Huh. It looks much more complicated than it needs to be, to me.
Actually looking more closely I really take exception to what it is doing with providing this._super() whilst in a method, to call the superclass method.
The code introduces a reliance on typeof==='function' (unreliable for some objects), Function#toString (argh, function decomposition is also unreliable), and deciding whether to wrap based on whether you've used the sequence of bytes _super in the function body (even if you've only used it in a string. and if you try eg. this['_'+'super'] it'll fail).
And if you're storing properties on your function objects (eg MyClass.myFunction.SOME_PRIVATE_CONSTANT, which you might do to keep namespaces clean) the wrapping will stop you from getting at those properties. And if an exception is thrown in a method and caught in another method of the same object, _super will end up pointing at the wrong thing.
All this is just to make calling your superclass's method-of-the-same name easier. But I don't think that's especially hard to do in JS anyway. It's too clever for its own good, and in the process making the whole less reliable. (Oh, and arguments.callee isn't valid in Strict Mode, though that's not really his fault since that occurred after he posted it.)
Here's what I'm using for classes at the moment. I don't claim that this is the “best” JS class system, because there are loads of different ways of doing it and a bunch of different features you might want to add or not add. But it's very lightweight and aims at being ‘JavaScriptic’, if that's a word. (It isn't.)
Function.prototype.makeSubclass= function() {
function Class() {
if (!(this instanceof Class))
throw 'Constructor function requires new operator';
if ('_init' in this)
this._init.apply(this, arguments);
}
if (this!==Object) {
Function.prototype.makeSubclass.nonconstructor.prototype= this.prototype;
Class.prototype= new Function.prototype.makeSubclass.nonconstructor();
}
return Class;
};
Function.prototype.makeSubclass.nonconstructor= function() {};
It provides:
protection against accidental missing new. The alternative is to silently redirect X() to new X() so missing new works. It's a toss-up which is best; I went for explicit error so that one doesn't get used to writing without new and causing problems on other objects not defined like that. Either way is better than the unacceptable JS default of letting this. properties fall onto window and mysteriously going wrong later.
an inheritable _init method, so you don't have to write a constructor-function that does nothing but call the superclass constructor function.
and that's really all.
Here's how you might use it to implement Resig's example:
var Person= Object.makeSubclass();
Person.prototype._init= function(isDancing) {
this.dancing= isDancing;
};
Person.prototype.dance= function() {
return this.dancing;
};
var Ninja = Person.makeSubclass();
Ninja.prototype._init= function() {
Person.prototype._init.call(this, false);
};
Ninja.prototype.swingSword= function() {
return true;
};
var p= new Person(true);
p.dance(); // => true
var n = new Ninja();
n.dance(); // => false
n.swingSword(); // => true
// Should all be true
p instanceof Person &&
n instanceof Ninja && n instanceof Person
Superclass-calling is done by specifically naming the method you want and calling it, a bit like in Python. You could add a _super member to the constructor function if you wanted to avoid naming Person again (so you'd say Ninja._super.prototype._init.call, or perhaps Ninja._base._init.call).

JavaScript is prototype based and not class based. My recommendation is not to fight it and declare subtypes the JS way:
MyDerivedObj.prototype = new MySuperObj();
MyDerivedObj.prototype.constructor = MyDerivedObj;

See how far you can get without using inheritance at all. Treat it as a performance hack (to be applied reluctantly where genuinely necessary) rather than a design principle.
In an a highly dynamic language like JS, it is rarely necessary to know whether an object is a Person. You just need to know if it has a firstName property or an eatFood method. You don't often need to know if an object is an array; if it has a length property and some other properties named after integers, that's usually good enough (e.g. the Arguments object). "If it walks like a duck and quacks like a duck, it's a duck."
// give back a duck
return {
walk: function() { ... },
quack: function() { ... }
};
Yes, if you're making very large numbers of small objects, each with dozens of methods, then by all means assign those methods to the prototype to avoid the overhead of creating dozens of slots in every instance. But treat that as a way of reducing memory overhead - a mere optimisation. And do your users a favour by hiding your use of new behind some kind of factory function, so they don't even need to know how the object is created. They just need to know it has method foo or property bar.
(And note that you won't really be modelling classical inheritance in that scenario. It's merely the equivalent of defining a single class to get the efficiency of a shared vtable.)