We Keep Coding

Inheritance with Object.create() method in javascript [duplicate]

Javascript 1.9.3 / ECMAScript 5 introduces Object.create, which Douglas Crockford amongst others has been advocating for a long time. How do I replace new in the code below with Object.create?
var UserA = function(nameParam) {
this.id = MY_GLOBAL.nextId();
this.name = nameParam;
}
UserA.prototype.sayHello = function() {
console.log('Hello '+ this.name);
}
var bob = new UserA('bob');
bob.sayHello();
(Assume MY_GLOBAL.nextId exists).
The best I can come up with is:
var userB = {
init: function(nameParam) {
this.id = MY_GLOBAL.nextId();
this.name = nameParam;
},
sayHello: function() {
console.log('Hello '+ this.name);
}
};
var bob = Object.create(userB);
bob.init('Bob');
bob.sayHello();
There doesn't seem to be any advantage, so I think I'm not getting it. I'm probably being too neo-classical. How should I use Object.create to create user 'bob'?

With only one level of inheritance, your example may not let you see the real benefits of Object.create.
This methods allows you to easily implement differential inheritance, where objects can directly inherit from other objects.
On your userB example, I don't think that your init method should be public or even exist, if you call again this method on an existing object instance, the id and name properties will change.
Object.create lets you initialize object properties using its second argument, e.g.:
var userB = {
sayHello: function() {
console.log('Hello '+ this.name);
}
};
var bob = Object.create(userB, {
'id' : {
value: MY_GLOBAL.nextId(),
enumerable:true // writable:false, configurable(deletable):false by default
},
'name': {
value: 'Bob',
enumerable: true
}
});
As you can see, the properties can be initialized on the second argument of Object.create, with an object literal using a syntax similar to the used by the Object.defineProperties and Object.defineProperty methods.
It lets you set the property attributes (enumerable, writable, or configurable), which can be really useful.

There is really no advantage in using Object.create(...) over new object.
Those advocating this method generally state rather ambiguous advantages: "scalability", or "more natural to JavaScript" etc.
However, I have yet to see a concrete example that shows that Object.create has any advantages over using new. On the contrary there are known problems with it. Sam Elsamman describes what happens when there are nested objects and Object.create(...) is used:
var Animal = {
traits: {},
}
var lion = Object.create(Animal);
lion.traits.legs = 4;
var bird = Object.create(Animal);
bird.traits.legs = 2;
alert(lion.traits.legs) // shows 2!!!
This occurs because Object.create(...) advocates a practice where data is used to create new objects; here the Animal datum becomes part of the prototype of lion and bird, and causes problems as it is shared. When using new the prototypal inheritance is explicit:
function Animal() {
this.traits = {};
}
function Lion() { }
Lion.prototype = new Animal();
function Bird() { }
Bird.prototype = new Animal();
var lion = new Lion();
lion.traits.legs = 4;
var bird = new Bird();
bird.traits.legs = 2;
alert(lion.traits.legs) // now shows 4
Regarding, the optional property attributes that are passed into Object.create(...), these can be added using Object.defineProperties(...).

Object.create is not yet standard on several browsers, for example IE8, Opera v11.5, Konq 4.3 do not have it. You can use Douglas Crockford's version of Object.create for those browsers but this doesn't include the second 'initialisation object' parameter used in CMS's answer.
For cross browser code one way to get object initialisation in the meantime is to customise Crockford's Object.create. Here is one method:-
Object.build = function(o) {
var initArgs = Array.prototype.slice.call(arguments,1)
function F() {
if((typeof o.init === 'function') && initArgs.length) {
o.init.apply(this,initArgs)
}
}
F.prototype = o
return new F()
}
This maintains Crockford prototypal inheritance, and also checks for any init method in the object, then runs it with your parameter(s), like say new man('John','Smith'). Your code then becomes:-
MY_GLOBAL = {i: 1, nextId: function(){return this.i++}} // For example
var userB = {
init: function(nameParam) {
this.id = MY_GLOBAL.nextId();
this.name = nameParam;
},
sayHello: function() {
console.log('Hello '+ this.name);
}
};
var bob = Object.build(userB, 'Bob'); // Different from your code
bob.sayHello();
So bob inherits the sayHello method and now has own properties id=1 and name='Bob'. These properties are both writable and enumerable of course. This is also a much simpler way to initialise than for ECMA Object.create especially if you aren't concerned about the writable, enumerable and configurable attributes.
For initialisation without an init method the following Crockford mod could be used:-
Object.gen = function(o) {
var makeArgs = arguments
function F() {
var prop, i=1, arg, val
for(prop in o) {
if(!o.hasOwnProperty(prop)) continue
val = o[prop]
arg = makeArgs[i++]
if(typeof arg === 'undefined') break
this[prop] = arg
}
}
F.prototype = o
return new F()
}
This fills the userB own properties, in the order they are defined, using the Object.gen parameters from left to right after the userB parameter. It uses the for(prop in o) loop so, by ECMA standards, the order of property enumeration cannot be guaranteed the same as the order of property definition. However, several code examples tested on (4) major browsers show they are the same, provided the hasOwnProperty filter is used, and sometimes even if not.
MY_GLOBAL = {i: 1, nextId: function(){return this.i++}}; // For example
var userB = {
name: null,
id: null,
sayHello: function() {
console.log('Hello '+ this.name);
}
}
var bob = Object.gen(userB, 'Bob', MY_GLOBAL.nextId());
Somewhat simpler I would say than Object.build since userB does not need an init method. Also userB is not specifically a constructor but looks like a normal singleton object. So with this method you can construct and initialise from normal plain objects.

TL;DR:
new Computer() will invoke the constructor function Computer(){} for one time, while Object.create(Computer.prototype) won't.
All the advantages are based on this point.
Sidenote about performance: Constructor invoking like new Computer() is heavily optimized by the engine, so it may be even faster than Object.create.

You could make the init method return this, and then chain the calls together, like this:
var userB = {
init: function(nameParam) {
this.id = MY_GLOBAL.nextId();
this.name = nameParam;
return this;
},
sayHello: function() {
console.log('Hello '+ this.name);
}
};
var bob = Object.create(userB).init('Bob');

Another possible usage of Object.create is to clone immutable objects in a cheap and effective way.
var anObj = {
a: "test",
b: "jest"
};
var bObj = Object.create(anObj);
bObj.b = "gone"; // replace an existing (by masking prototype)
bObj.c = "brand"; // add a new to demonstrate it is actually a new obj
// now bObj is {a: test, b: gone, c: brand}
Notes: The above snippet creates a clone of an source object (aka not a reference, as in cObj = aObj). It benefits over the copy-properties method (see 1), in that it does not copy object member properties. Rather it creates another -destination- object with it's prototype set on the source object. Moreover when properties are modified on the dest object, they are created "on the fly", masking the prototype's (src's) properties.This constitutes a fast an effective way of cloning immutable objects.
The caveat here is that this applies to source objects that should not be modified after creation (immutable). If the source object is modified after creation, all the clone's unmasked properties will be modified, too.
Fiddle here(http://jsfiddle.net/y5b5q/1/) (needs Object.create capable browser).

I think the main point in question - is to understand difference between new and Object.create approaches. Accordingly to this answer and to this video new keyword does next things:
Creates new object.
Links new object to constructor function (prototype).
Makes this variable point to the new object.
Executes constructor function using the new object and implicit perform return this;
Assigns constructor function name to new object's property constructor.
Object.create performs only 1st and 2nd steps!!!
In code example provided in question it isn't big deal, but in next example it is:
var onlineUsers = [];
function SiteMember(name) {
this.name = name;
onlineUsers.push(name);
}
SiteMember.prototype.getName = function() {
return this.name;
}
function Guest(name) {
SiteMember.call(this, name);
}
Guest.prototype = new SiteMember();
var g = new Guest('James');
console.log(onlineUsers);
As side effect result will be:
[ undefined, 'James' ]
because of Guest.prototype = new SiteMember();
But we don't need to execute parent constructor method, we need only make method getName to be available in Guest.
Hence we have to use Object.create.
If replace Guest.prototype = new SiteMember();
to Guest.prototype = Object.create(SiteMember.prototype); result be:
[ 'James' ]

Sometimes you cannot create an object with NEW but are still able to invoke the CREATE method.
For example: if you want to define a Custom Element it must derive from HTMLElement.
proto = new HTMLElement //fail :(
proto = Object.create( HTMLElement.prototype ) //OK :)
document.registerElement( "custom-element", { prototype: proto } )

The advantage is that Object.create is typically slower than new on most browsers
In this jsperf example, in a Chromium, browser new is 30 times as fast as Object.create(obj) although both are pretty fast. This is all pretty strange because new does more things (like invoking a constructor) where Object.create should be just creating a new Object with the passed in object as a prototype (secret link in Crockford-speak)
Perhaps the browsers have not caught up in making Object.create more efficient (perhaps they are basing it on new under the covers ... even in native code)

Summary:
Object.create() is a Javascript function which takes 2 arguments and returns a new object.
The first argument is an object which will be the prototype of the newly created object
The second argument is an object which will be the properties of the newly created object
Example:
const proto = {
talk : () => console.log('hi')
}
const props = {
age: {
writable: true,
configurable: true,
value: 26
}
}
let Person = Object.create(proto, props)
console.log(Person.age);
Person.talk();
Practical applications:
The main advantage of creating an object in this manner is that the prototype can be explicitly defined. When using an object literal, or the new keyword you have no control over this (however, you can overwrite them of course).
If we want to have a prototype The new keyword invokes a constructor function. With Object.create() there is no need for invoking or even declaring a constructor function.
It can Basically be a helpful tool when you want create objects in a very dynamic manner. We can make an object factory function which creates objects with different prototypes depending on the arguments received.

You have to make a custom Object.create() function. One that addresses Crockfords concerns and also calls your init function.
This will work:
var userBPrototype = {
init: function(nameParam) {
this.name = nameParam;
},
sayHello: function() {
console.log('Hello '+ this.name);
}
};
function UserB(name) {
function F() {};
F.prototype = userBPrototype;
var f = new F;
f.init(name);
return f;
}
var bob = UserB('bob');
bob.sayHello();
Here UserB is like Object.create, but adjusted for our needs.
If you want, you can also call:
var bob = new UserB('bob');

While Douglas Crockford used to be a zealous advocate of Object.create() and he is basically the reason why this construct actually is in javascript, he no longer has this opinion.
He stopped using Object.create, because he stopped using this keyword altogether as it causes too much trouble. For example, if you are not careful it can easily point to the global object, which can have really bad consequences. And he claims that without using this Object.create does not make sense anymore.
You can check this video from 2014 where he talks at Nordic.js:
https://www.youtube.com/watch?v=PSGEjv3Tqo0

new and Object.create serve different purposes. new is intended to create a new instance of an object type. Object.create is intended to simply create a new object and set its prototype. Why is this useful? To implement inheritance without accessing the __proto__ property. An object instance's prototype referred to as [[Prototype]] is an internal property of the virtual machine and is not intended to be directly accessed. The only reason it is actually possible to directly access [[Prototype]] as the __proto__ property is because it has always been a de-facto standard of every major virtual machine's implementation of ECMAScript, and at this point removing it would break a lot of existing code.
In response to the answer above by 7ochem, objects should absolutely never have their prototype set to the result of a new statement, not only because there's no point calling the same prototype constructor multiple times but also because two instances of the same class can end up with different behavior if one's prototype is modified after being created. Both examples are simply bad code as a result of misunderstanding and breaking the intended behavior of the prototype inheritance chain.
Instead of accessing __proto__, an instance's prototype should be written to when an it is created with Object.create or afterward with Object.setPrototypeOf, and read with Object.getPrototypeOf or Object.isPrototypeOf.
Also, as the Mozilla documentation of Object.setPrototypeOf points out, it is a bad idea to modify the prototype of an object after it is created for performance reasons, in addition to the fact that modifying an object's prototype after it is created can cause undefined behavior if a given piece of code that accesses it can be executed before OR after the prototype is modified, unless that code is very careful to check the current prototype or not access any property that differs between the two.
Given
const X = function (v) { this.v = v };
X.prototype.whatAmI = 'X';
X.prototype.getWhatIAm = () => this.whatAmI;
X.prototype.getV = () => this.v;
the following VM pseudo-code is equivalent to the statement const x0 = new X(1);:
const x0 = {};
x0.[[Prototype]] = X.prototype;
X.prototype.constructor.call(x0, 1);
Note although the constructor can return any value, the new statement always ignores its return value and returns a reference to the newly created object.
And the following pseudo-code is equivalent to the statement const x1 = Object.create(X.prototype);:
const x0 = {};
x0.[[Prototype]] = X.prototype;
As you can see, the only difference between the two is that Object.create does not execute the constructor, which can actually return any value but simply returns the new object reference this if not otherwise specified.
Now, if we wanted to create a subclass Y with the following definition:
const Y = function(u) { this.u = u; }
Y.prototype.whatAmI = 'Y';
Y.prototype.getU = () => this.u;
Then we can make it inherit from X like this by writing to __proto__:
Y.prototype.__proto__ = X.prototype;
While the same thing could be accomplished without ever writing to __proto__ with:
Y.prototype = Object.create(X.prototype);
Y.prototype.constructor = Y;
In the latter case, it is necessary to set the constructor property of the prototype so that the correct constructor is called by the new Y statement, otherwise new Y will call the function X. If the programmer does want new Y to call X, it would be more properly done in Y's constructor with X.call(this, u)

new Operator
This is used to create object from a constructor function
The new keywords also executes the constructor function
function Car() {
console.log(this) // this points to myCar
this.name = "Honda";
}
var myCar = new Car()
console.log(myCar) // Car {name: "Honda", constructor: Object}
console.log(myCar.name) // Honda
console.log(myCar instanceof Car) // true
console.log(myCar.constructor) // function Car() {}
console.log(myCar.constructor === Car) // true
console.log(typeof myCar) // object
Object.create
You can also use Object.create to create a new object
But, it does not execute the constructor function
Object.create is used to create an object from another object
const Car = {
name: "Honda"
}
var myCar = Object.create(Car)
console.log(myCar) // Object {}
console.log(myCar.name) // Honda
console.log(myCar instanceof Car) // ERROR
console.log(myCar.constructor) // Anonymous function object
console.log(myCar.constructor === Car) // false
console.log(typeof myCar) // object

I prefer a closure approach.
I still use new.
I don't use Object.create.
I don't use this.
I still use new as I like the declarative nature of it.
Consider this for simple inheritance.
window.Quad = (function() {
function Quad() {
const wheels = 4;
const drivingWheels = 2;
let motorSize = 0;
function setMotorSize(_) {
motorSize = _;
}
function getMotorSize() {
return motorSize;
}
function getWheelCount() {
return wheels;
}
function getDrivingWheelCount() {
return drivingWheels;
}
return Object.freeze({
getWheelCount,
getDrivingWheelCount,
getMotorSize,
setMotorSize
});
}
return Object.freeze(Quad);
})();
window.Car4wd = (function() {
function Car4wd() {
const quad = new Quad();
const spareWheels = 1;
const extraDrivingWheels = 2;
function getSpareWheelCount() {
return spareWheels;
}
function getDrivingWheelCount() {
return quad.getDrivingWheelCount() + extraDrivingWheels;
}
return Object.freeze(Object.assign({}, quad, {
getSpareWheelCount,
getDrivingWheelCount
}));
}
return Object.freeze(Car4wd);
})();
let myQuad = new Quad();
let myCar = new Car4wd();
console.log(myQuad.getWheelCount()); // 4
console.log(myQuad.getDrivingWheelCount()); // 2
console.log(myCar.getWheelCount()); // 4
console.log(myCar.getDrivingWheelCount()); // 4 - The overridden method is called
console.log(myCar.getSpareWheelCount()); // 1
Feedback encouraged.

What's the recommended way of creating objects in NodeJS?

I'm building a composite for request module, however I'm not sure what's the best practice regarding building objects in JS for Node.
Option 1:
function RequestComposite(request) {
return {
get: function (url) { return request.get(url); }
}
}
var comp = RequestComposite(request);
Note: I know that i should call a CB in async way, but for the ease of explaination I return it...
Option 2:
function RequestComposite(request) {
this.request = request;
}
RequestComposite.prototype.get = function (url) { return this.request.get(url); };
var comp = new RequestComposite(request);
Option 3:
var RequestComposite = {
init: function (request) { this.request = request; },
get: function (url) { return request.get(url); }
}
var comp = Object.create(RequestComposite).init(request);
I tried to find my way around, however I got even more confused about how should I use objects...
Would the answer be different if I want to use objects for browsers?
Thanks.

The most efficient way is the following:
Put all the essential initialisation in the constructor (e.g. validate constructor parameters, set properties, etc).
Set methods in the .prototype property of the constructor. Why? Because this prevents from re-writing each method each time you create an object. This way you recycle the same prototype for each object you create. Efficient in memory and sparing coding time.
Do not use closures for private properties. Why? It is slow, and prevents you from using this object in an inheritance chain (the pseudo-private vars don't belong to the object, they're just accessible). It is instead common practice to use an underscore when declaring an object property, to indicate it is a _private property that should not be accessed from outside.
Use new instead of Object.create. It's easier to remember if you are used to other OOP languages; and at the end new uses Object.create under the hood.
In other words, something like this:
var Person = function (name) {
this._name = name;
};
Person.prototype.sayHello = function () {
alert('My name is: ' + this._name);
};
var john = new Person('John');
john.sayHello();
EDIT
Some extra information:
Object.create vs new. Benchmark here. Although the question is for Node.js, I think the same behaviour is to be expected. (any correction is welcome)
Closures to emulate private properties: You can read about in this question.. The point that the private/closure properties do not belong to the object is a programming fact: they are accessible by the object methods but do not belong to the object. When using inheritance, that is a big mess. Besides, only methods that are declared in the constructor have access to the closure. Methods defined in the prototype do not.
Defining methods in the constructor or the prototype property: read this question, and take a look of this benchmark
EDIT 15/04/2016
The points I made here three years ago are still right from a performance point of view, but my opinion about what is the "recommended way" has changed a little in the meanwhile. Factory functions are in general a good option, which would be the OP's first approach. Just an example:
function Person(name) {
return {
sayHello: function () { alert('My name is: ' + name); }
};
}
and then just do:
var p = Person('John');
In this case you trade flexibility (no new coupling, ease of composition with other "mix-ins") and simplicity (no this mess, easy object instantiation) for some speed and memory. In general they are perfectly valid. If you have performance issues, and those are because of this way of creating objects, revert to another method. The Object.create approach is also good, falling somehow in the middle of new and factory functions (side note: the new class syntax is syntactic sugar for new+ prototype)
Summing up: my recommended way is starting from the simplest and easiest way of creating objects (factory functions) and then fall to other methods when you hit performance issues (which in most of cases is never).

There are many ways to create "Class" and "Object" in JS. I prefer this way:
var MyObject =
function(args) {
// Private
var help = "/php/index.php?method=getHelp";
var schedule = "/php/index.php?method=getSchedules";
var ajax = function(url, callback, type) {
//....
}
// Public
this.property = 0;
this.getInfo = function() {
// ...
}
// Constructor
function(data) {
this.property = data;
}(args);
};
var o = new MyObject();

Note: If you are more familiar with OOP syntax, you can also use class which is just syntactical sugar over existing prototype-based way.
Performance Comparison between 4 ways of creating object - with constructor (Chrome 61 - https://jsperf.com/create-object-ways)
Option A: Using return (Fastest 3x)
Option B: Using {key:value} (1.5x)
Option C: Using prototype (1x) <- Base
Option D: Using class (1.02x)
Option A seams to perform best. Note that some of the performance boost is because it avoids use of new or object.create. So just to have a fair trial, here is another test between method-only objects without constructor and properties.
Performance Comparison between 4 ways of creating methods-only object (Chrome 61 - https://jsperf.com/create-static-object-ways)
Option A: Using return (3.2x)
Option B: Using {key:value} (Fastest 3.3x)
Option C: Using prototype (1.8x)
Option D: Using class (1.9x)
Option B outperformed Option A a little. Also the bottleneck caused by object.create was more then new.
Best Practice
Option A (using return) is best performing in both the scenarios. This way can get little messy if you have many methods and properties.
I prefer to divide constructor & properties in separate object using Option A and methods in another object using Option B. This approach does need to send an extra instance reference in parameters but can be useful if you have multiple objects using same properties & constructor (Some OOP inheritance can also be achieved).
Example:
// Constructor & Properties Object (Using option A)
var UserData = function(request){
// Constructor
if ( request.name )
var name = request.name;
else
var name = 'Not Available';
if ( request.age )
var age = request.age;
else
var age = null;
// Return properties
return {
userName: name,
userAge: age
};
};
// Object methods (Using Option B)
var Adults = {
printName: function(instance){ // Read propery example
console.log( 'Mr. ' + instance.userName );
},
changeName: function(instance, newName){ // Write property example
instance.userName = newName;
},
foo: function(){
console.log( 'foo' );
}
};
// Object methods (Using Option B)
var Children = {
printName: function(instance){
console.log( 'Master ' + instance.userName );
},
bar: function(){
console.log( 'bar' );
}
}
// Initialize
var userData = UserData ( {name: 'Doe', age: 40} );
// Call methods
Adults.printName(userData); // Output 'Mr. Doe'
Children.printName(userData); // Output 'Master Doe'
Adults.foo(); // Output 'foo'
Children.bar(); // Output 'bar'
Adults.changeName(userData, 'John');
Adults.printName(userData); // Output 'Mr. John'

How to achieve pseudo-classical inheritance right on the class declaration? [duplicate]

This question already has answers here:
How to implement C# access modifiers in javascript?
(5 answers)
Closed 1 year ago.
Note:
As the answers tell, the code proposed in the question does NOT really achieve inheritance(otherwise it becomes an answer rather than a question .. ) due to some issues described in the question and in my comments. It works as expected as a fake of inheritance(and not even prototypal).
Summary
In short, make it as similar as we are writing a general OO language rather than javascript, but keep the inheritance be correct.
The story
Object.create is a good way to achieve prototypal inheritance, but it's a bit confusing to a typed brain and new fans.
There are various ways that we can write javascript code more like we are writing other OO languages with the pseudo-classical pattern. As it's pseudo-classical, we must deal with the underlying prototypal inheritance of javascript correctly.
What I want to find is an approach that the pseudo-classical inheritance can be achieved right on the class declaration. The code for demonstration is put at the rear of the post, it works as expected, however, there are some annoying things:
I cannot get rid of return in the class declaration or the inheritance won't work.
I have no way except pass this in the class declaration to make the returning closure know what is this.
I also want to get rid of function (instance, _super) {, but not yet have a good idea.
The static(own properties) of a class are not inherited.
A solution would be more of some syntactic sugar than the existing frameworks, a good pattern is applicable.
The _extends function:
function _extends(baseType) {
return function (definition) {
var caller=arguments.callee.caller;
var instance=this;
if(!(instance instanceof baseType)) {
(caller.prototype=new baseType()).constructor=caller;
instance=new caller();
}
var _super=function () {
baseType.apply(instance, arguments);
};
definition(instance, _super);
return instance;
};
}
The Abc class:
function Abc(key, value) {
return _extends(Object).call(this, function (instance, _super) {
instance.What=function () {
alert('What');
};
instance.getValue=function () {
return 333+Number(value);
};
instance.Value=instance.getValue();
instance.Key=key;
});
}
The Xyz class:
function Xyz(key, value) {
return _extends(Abc).call(this, function (instance, _super) {
_super(key, value);
instance.That=function () {
alert('That');
};
});
}
Example code:
var x=new Xyz('x', '123');
alert([x.Key, x.Value].join(': ')+'; isAbc: '+(x instanceof Abc));
var y=new Xyz('y', '456');
alert([y.Key, y.Value].join(': ')+'; isAbc: '+(y instanceof Abc));
var it=new Abc('it', '789');
alert([it.Key, it.Value].join(': ')+'; isAbc: '+(it instanceof Abc));
alert([it.Key, it.Value].join(': ')+'; isXyz: '+(it instanceof Xyz));
x.What();
y.That();
it.What();
it.That(); // will throw; it is not Xyz and does not have That method

No. No. No. This won't do. You're doing inheritance in JavaScript all wrong. Your code gives me migraines.
Creating a Pseudo-Classical Inheritance Pattern in JavaScript
If you want something similar to classes in JavaScript then there are a lot of libraries out there which provide it to you. For example using augment you could restructure your code as follows:
var augment = require("augment");
var ABC = augment(Object, function () {
this.constructor = function (key, value) {
this.key = key;
this.value = value;
};
this.what = function () {
alert("what");
};
});
var XYZ = augment(ABC, function (base) {
this.constructor = function (key, value) {
base.constructor.call(this, key, value);
};
this.that = function () {
alert("that");
};
});
I don't know about you but to me this looks a lot like classical inheritance in C++ or Java. If this solves your problem, great! If is doesn't then continue reading.
Prototype-Class Isomorphism
In a lot of ways prototypes are similar to classes. In fact prototypes and classes are so similar that we can use prototypes to model classes. First let's take a look at how prototypal inheritance really works:
The above picture was taken from the following answer. I suggest you read it carefully. The diagram shows us:
Every constructor has a property called prototype which points to the prototype object of the constructor function.
Every prototype has a property called constructor which points to the constructor function of the prototype object.
We create an instance from a constructor function. However the instance actually inherits from the prototype, not the constructor.
This is very useful information. Traditionally we've always created a constructor function first and then we've set its prototype properties. However this information shows us that we may create a prototype object first and then define the constructor property on it instead.
For example, traditionally we may write:
function ABC(key, value) {
this.key = key;
this.value = value;
}
ABC.prototype.what = function() {
alert("what");
};
However using our newfound knowledge we may write the same thing as:
var ABC = CLASS({
constructor: function (key, value) {
this.key = key;
this.value = value;
},
what: function () {
alert("what");
}
});
function CLASS(prototype) {
var constructor = prototype.constructor;
constructor.prototype = prototype;
return constructor;
}
As you can see encapsulation is easy to achieve in JavaScript. All you need to do is think sideways. Inheritance however is a different issue. You need to do a little more work to achieve inheritance.
Inheritance and Super
Take a look at how augment achieves inheritance:
function augment(body) {
var base = typeof this === "function" ? this.prototype : this;
var prototype = Object.create(base);
body.apply(prototype, arrayFrom(arguments, 1).concat(base));
if (!ownPropertyOf(prototype, "constructor")) return prototype;
var constructor = prototype.constructor;
constructor.prototype = prototype;
return constructor;
}
Notice that the last three lines are the same as that of CLASS from the previous section:
function CLASS(prototype) {
var constructor = prototype.constructor;
constructor.prototype = prototype;
return constructor;
}
This tells us that once we have a prototype object all we need to do is get its constructor property and return it.
The first three lines of augment are used to:
Get the base class prototype.
Create a derived class prototype using Object.create.
Populate the derived class prototype with the specified properties.
That's all that there is to inheritance in JavaScript. If you want to create your own classical inheritance pattern then you should be thinking along the same lines.
Embracing True Prototypal Inheritance
Every JavaScript programmer worth their salt will tell you that prototypal inheritance is better than classical inheritance. Nevertheless newbies who come from a language with classical inheritance always try to implement classical inheritance on top of prototypal inheritance, and they usually fail.
They fail not because it's not possible to implement classical inheritance on top of prototypal inheritance but because to implement classical inheritance on top of prototypal inheritance you first need to understand how true prototypal inheritance works.
However once you understand true prototypal inheritance you'll never want to go back to classical inheritance. I too tried to implement classical inheritance on top of prototypal inheritance as a newbie. Now that I understand how true prototypal inheritance works however I write code like this:
function extend(self, body) {
var base = typeof self === "function" ? self.prototype : self;
var prototype = Object.create(base, {new: {value: create}});
return body.call(prototype, base), prototype;
function create() {
var self = Object.create(prototype);
return prototype.hasOwnProperty("constructor") &&
prototype.constructor.apply(self, arguments), self;
}
}
The above extend function is very similar to augment. However instead of returning the constructor function it returns the prototype object. This is actually a very neat trick which allows static properties to be inherited. You can create a class using extend as follows:
var Abc = extend(Object, function () {
this.constructor = function (key, value) {
this.value = 333 + Number(value);
this.key = key;
};
this.what = function () {
alert("what");
};
});
Inheritance is just as simple:
var Xyz = extend(Abc, function (base) {
this.constructor = function (key, value) {
base.constructor.call(this, key, value);
};
this.that = function () {
alert("that");
};
});
Remember however that extend does not return the constructor function. It returns the prototype object. This means that you can't use the new keyword to create an instance of the class. Instead you need to use new as a method, as follows:
var x = Xyz.new("x", "123");
var y = Xyz.new("y", "456");
var it = Abc.new("it", "789");
This is actually a good thing. The new keyword is considered harmful and I strongly recommend you to stop using it. For example it's not possible to use apply with the new keyword. However it is possible to use apply with the new method as follows:
var it = Abc.new.apply(null, ["it", "789"]);
Since Abc and Xyz are not constructor functions we can't use instanceof to test whether an object is an instance of Abc or Xyz. However that's not a problem because JavaScript has a method called isPrototypeOf which tests whether an object is a prototype of another object:
alert(x.key + ": " + x.value + "; isAbc: " + Abc.isPrototypeOf(x));
alert(y.key + ": " + y.value + "; isAbc: " + Abc.isPrototypeOf(y));
alert(it.key + ": " + it.value + "; isAbc: " + Abc.isPrototypeOf(it));
alert(it.key + ": " + it.value + "; isXyz: " + Xyz.isPrototypeOf(it));
In fact isPrototypeOf is more powerful than instanceof because it allows us to test whether one class extends another class:
alert(Abc.isPrototypeOf(Xyz)); // true
Besides this minor change everything else works just like it did before:
x.what();
y.that();
it.what();
it.that(); // will throw; it is not Xyz and does not have that method
See the demo for yourself: http://jsfiddle.net/Jee96/
What else does true prototypal inheritance offer? One of the biggest advantages of true prototypal inheritance is that there's no distinction between normal properties and static properties allowing you to write code like this:
var Xyz = extend(Abc, function (base) {
this.empty = this.new();
this.constructor = function (key, value) {
base.constructor.call(this, key, value);
};
this.that = function () {
alert("that");
};
});
Notice that we can create instances of the class from within the class itself by calling this.new. If this.constructor is not yet defined then it returns a new uninitialized instance. Otherwise it returns a new initialized instance.
In addition because Xyz is the prototype object we can access Xyz.empty directly (i.e. empty is a static property of Xyz). This also means that static properties are automatically inherited and are no different from normal properties.
Finally, because the class is accessible from within the class definition as this, you can created nested classes which inherit from the class which they are nested within by using extend as follows:
var ClassA = extend(Object, function () {
var ClassB = extend(this, function () {
// class definition
});
// rest of the class definition
alert(this.isPrototypeOf(ClassB)); // true
});
See the demo for yourself: http://jsfiddle.net/Jee96/1/

There's an exhaustive tutorial on how to do what you're after.
oop-concepts
pseudo-classical-pattern
all-one-constructor-pattern

I know this doesn't answer your question because as far as I know there is no good way to put everything in the function constructor and have it use prototype.
As I've commented; if you have trouble with the JavaScript syntax then typescript could be a good alternative.
Here is a helper function that I use for inheritance and overriding (calling super) using JavaScript (without Object.create)
var goog={};//inherits from closure library base
//http://docs.closure-library.googlecode.com/git/closure_goog_base.js.source.html#line1466
// with modifications for _super
goog.inherits = function(childCtor, parentCtor) {
function tempCtor() {};
tempCtor.prototype = parentCtor.prototype;
childCtor.prototype = new tempCtor();
childCtor.prototype.constructor = childCtor;
// modified _super
childCtor.prototype._super = parentCtor.prototype;
};
// Parent class dev
var Parent = function(){};
Parent.prototype.sayHi=function(){
console.log("hi from Parent");
}
// end class
// Child class dev
var Child = function(){}
goog.inherits(Child,Parent);
Child.prototype.sayHi=function(){
//_super only works on parent.prototype
//this is where functions are usually defined
//have to add this. to call _super as well
this._super.sayHi();
console.log("hi from Child");
}
// end Child
//code to test
var c = new Child();
c.sayHi();//hi from Parent and hi from Child
Even if you find a way to write helper functions and make JS constructor functions look like Java classes you have to understand prototype.

You can always try jOOP, though it does require jQuery.
https://github.com/KodingSykosis/jOOP
var myClass = $.cls({
main: function() {
$('body').append('My App is loaded <br/>');
}
});
var mySecondClass = $.cls({
main: function() {
this._super();
$('body').append('My Second App is loaded <br/>');
}
}, myClass);
var app = new mySecondClass();
http://jsfiddle.net/kodingsykosis/PrQWu/

I believe you are looking for more functionality than this, but if you want to just inherit a bunch of methods from another class you could do this
http://cdpn.io/Jqhpc
var Parent = function Parent () {
this.fname = 'Bob';
this.lname = 'Jones';
};
Parent.prototype.getFname = function getFname () {
return this.fname;
};
Parent.prototype.getLname = function getLname () {
return this.lname;
};
var Child = function Child () {
this.fname = 'Jim';
};
Child.prototype = Parent.prototype;
var child = new Child();
document.write(child.getFname()); //=> Jim

How to extend a class in JavaScript

I'm working on a chess game built in JavaScript. I'm taking an object-oriented approach to it and am having some difficulty working with JavaScript's inheritance. I want there to be a "Piece" abstract class that holds some fields and basic getters/setters such as is this piece black or white. I then want to have classes for each type of piece that I can instantiate like so:
var pieceOne = new Pawn();
The Pawn() should have all the fields and methods of Piece but have its own method for movement, and additional fields (such as whether or not it has moved yet, as this doesn't matter for most pieces). Here's my current Piece class:
//This object specifies basic information about pieces.
"use strict";
function Piece(color, type, captured, hasMoved) {
this.color = color;
this.type = type;
this.captured = captured;
this.hasMoved = hasMoved;
this.image = color + "_" + type + ".svg";
}
Piece.prototype.getImage = function getImage(){
return this.image;
}
Piece.prototype.isCaptured = function isCaptured(){
return this.captured;
};
I know if I am going to make a subclass for every kind of piece that I'd probably eliminate the "type" field, but how could I make a Pawn subclass? Something like this?
function Pawn() = new Piece(color, captured, hasMoved);
Pawn.prototype.getLegalMoves = function getLegalMoves(){
//return legal moves
}
var pieceOne = new Pawn("black", false, false);

Extending a class can be done in different ways. The simplest method to extend an class is to use Object.create method. This is common method which is used to achieve abstraction (Link to my blog). Let's give an example of the Object.create method as follows.
var Logger = { log : function(log){} }
var ConsoleLogger = function() {};
ConsoleLogger.prototype = Object.create(Logger);

If you are willing to take an object oriented approach on JS I would recommend you to follow the power constructor pattern.
Basically you have a function that creates objects for you and take advantage of the closures to hide the internal properties (fields or methods).
function myObject(){
var that={};
var myPrivateField;
var myPrivateFunction=function(){
}
that.myPublicMethod=function(){
}
return that;
}
Then you can just call the method myObject() and you will get a new object of this type.
You can extend this example to use inheritance by just calling the power constructor of another object and then use object augmentation. Take a look at the example of parasatic inheritance of Douglas Crockford.

You can call Piece's constructor from Pawn and have that constructor operate on the Pawn instance:
function Pawn(/* args... */) {
Piece.call(this, color, type, captured, hasMoved);
/* Pawn-specific constructor code... */
}

I believe it's just a matter of setting the prototype of the specific piece constructors to an instance of Piece. For example:
Pawn.prototype = new Piece("", false, false);
However, this will not call the Piece (super) constructor every time you instantiate a new Pawn, so you'll have to manually assign color, type, etc. from the Pawn constructor:
-- EDIT --
You might prefer this instead: Javascript inheritance: call super-constructor or use prototype chain?

Take a look at this: https://github.com/haroldiedema/joii
var BaseClass = function()
{
this.some_var = "foobar";
/**
* #return string
*/
this.someMethod = function() {
return this.some_var;
}
};
var MyClass = new Class({ extends: BaseClass }, function()
{
/**
* #param string value
*/
this.__construct = function(value)
{
this.some_var = value;
}
})
Usage:
var obj = new MyClass("Hello World!");
console.log( obj.someMethod() ); // Hello World!

Pros and cons of inheritance modeling in Javascript?

I realize that Javascript does not have classes and is not built to have classical OOP inheritance. But I find such patterns so useful that I wanted to build a simple way to model that kind of behavior, ideally while leveraging the best parts of Javascript's flexibility. What are the pros and cons of the following approach?
I have the following functions in my custom library:
function inherit(superClass, args, instance) {
var subClass = inherit.caller;
var o = new superClass(args);
for(p in o) {
if(o.hasOwnProperty(p)) init(instance, p, o[p]);
else init(subClass.prototype, p, o[p]);
}
}
function isUndefined(x) {var u; return x === u;}
// sets p to value only if o[p] is undefined
function init(o, p, value) {if(isUndefined(o[p])) o[p] = value;}
This setup requires two conventions:
Functions that are modelling classes must take one argument: an object with named properties
Functions wishing to "inherit" from another must call the inherit function.
Here's an example of what you get as a result (paste into the Firebug command line, along with the library functions, to see it in action):
function SuperClass(args) {
this.x = args.x;
}
SuperClass.prototype.p = 'SuperClass prototype property p';
function SubClass(args) {
inherit(SuperClass, args, this);
this.y = args.y;
}
SubClass.prototype.q = 'SubClass prototype property q';
var o = new SubClass({
x: 'x set in SuperClass',
y: 'y set in SubClass'
});
console.dir(o); // correctly has properties x, y, p, and q
['x', 'y', 'p', 'q'].forEach(function(prop) {
// true for x and y, false for p and q
console.log("o.hasOwnProperty('" + prop + "')", o.hasOwnProperty(prop));
});
console.log("o instanceof SubClass: ", o instanceof SubClass); // true
console.log("o instanceof SuperClass: ", o instanceof SuperClass); // false
I am aware of the following cons:
Modifying the super class prototype will not affect your instance object, as you might expect from prototype-style inheritance
The instance object will not register as instanceof the super class (although it will still quack like one)
The argument conventions might be annoying
and pros:
Requires only one function call (easy to implement)
Differentiates between prototype properties and instance properties
Arguments passed to the sub class are also passed to the super class
Instance properties set by the super class constructor are immediately available in the sub class constructor
Multiple inheritance is easy, just call inherit multiple times in your sub class
Doesn't over-write existing properties of the sub class
Pros 3 - 6 specifically make this method more useful for me than the SubClass.prototype = new SuperClass() method. Other methods, like dojo's class modelling, are much more complicated, I think unnecessarily so.
So, tell me what you think. And if someone else has done this before, please let me know, I haven't intended to duplicate any ideas.

Those coming here to see simple and probably best way to do inheritance in javascript please read the following, its so much simpler than everything else I've scanned through:
http://javascript.crockford.com/prototypal.html
if (typeof Object.create !== 'function') {
Object.create = function (o) {
function F() {}
F.prototype = o;
return new F();
};
}
N.B: Object.create is now part of javascript in newer browsers, but by adding the above the following also works in older browsers.
newObject = Object.create(oldObject);

You might want to look at what John Resig has done with JavaScript inheritance: http://ejohn.org/blog/simple-javascript-inheritance/
It's the best attempt at Javascript inheritance that I've seen.

You know the cons of what you posted.... So take a look at my blog for a thorough explanation of what I think is the best way while describing the flaws of other patterns
http://js-bits.blogspot.com/2010/08/javascript-inheritance-done-right.html
Example:
//Abstraxct base class
function Animal(name) {
this.name = name;
}
Animal.prototype.sayMyName = function () {
console.log(this.getWordsToSay() + " " + this.name);
}
Animal.prototype.getWordsToSay = function () {} // abstract
// --------------------------------
function Dog(name) {
// Call the parent's constructor
Animal.call(this, name);
}
extend(Dog, Animal, {
getWordsToSay: function(){
return "Ruff Ruff";
}
});
The code I posted is an example syntax. The blog posts goes into details about how to add syntactic sugar.
The important things are:
new Dog("Lassie") instanceof Animal // true
The Animal constructor is not called just to setup inheritance
var dog = new Dog("Lassie"); Animal.prototype.blah = 5; dog.blah == 5; //outputs true