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How to implement classical class inheritance through prototypes

I would like to implement the following behavior in JS. Please note that the syntax is symbolic.
This is my parent class
class = TList {
FList: array;
function AddElement(Ele) {
Flist.Add(Ele)
};
function RemoveEle(Ele) {
FList.Remove(Ele)
};
}
Now I'm going to inherit from this class. My child class should automatically have all the properties of the parent and should be able to extend them without rewriting the code.
class = TAlertList(inherit from TList) {
function AddElement(Ele) {
Alert('element will be added');
call.parent.AddElement(Ele)
};
function RemoveElement(Ele) {
call.parent.RemoveElement(Ele);
Alert('element removed');
}
}
Please note how I inherit the parent methods at places I wish.
Now I should be able to create an object from my child class and do the following.
MyAlertList = new TAlertList;
MyAlertList.Add('hello');
console.log(MyAlertList.FList);
I should be able to inherit more child classes from TAlertList and be able to change the existing behavior. I need to do this in pure ES5 without using any libraries. Standard OOP practices are expected.

Please note that the TList constructor should be applied to the TAlertList instance;
ES5, first set up the base constructor
function TList() {
this.Flist = [];
// ...
}
TList.prototype = {
constructor: TList,
AddElement: function AddElement(Ele) {
this.Flist.push(Ele);
},
RemoveEle: function RemoveEle(Ele) {
var i = this.Flist.lastIndexOf(Ele);
if (i !== -1)
this.Flist.splice(i, 1);
}
};
Next set up the constructor which extends it, see how this means calling the base constructor on the instance being created by the extended constructor and creating a prototype object which inherits the prototype of the base constructor
function TAlertList() {
// construct from base
TList.call(this);
// further construct
// ...
}
TAlertList.prototype = Object.create(TList.prototype);
TAlertList.prototype.constructor = TAlertList;
// depending on how you want to reference stuff
TAlertList.prototype.AddElement = function AddElement(Ele) {
alert('element will be added');
TList.prototype.AddElement.call(this, Ele);
};
TAlertList.prototype.RemoveElement = function RemoveElement(Ele) {
TList.prototype.RemoveEle.call(this, Ele);
alert('element removed');
};
ES6 syntax makes use of the super keyword
class TList {
constructor() {
this.FList = [];
}
AddElement(Ele) {
this.Flist.push(Ele);
}
RemoveEle(Ele) {
var i = this.Flist.lastIndexOf(Ele);
if (i !== -1)
this.Flist.splice(i, 1);
}
}
class TAlertList extends TList {
constructor() {
super();
}
AddElement(Ele) {
alert('element will be added');
super.AddElement(Ele);
}
RemoveElement(Ele) {
super.RemoveEle(Ele);
alert('element removed');
}
}
Back to ES5, generalising as a factory so you can see a sort of algorithm of how to do it
function extend(baseConstructor, extendedConstructor, prototypeLayer) {
function Constructor() {
var i = 0, j = 0, args = Array.prototype.slice.call(arguments);
i = j, j += baseConstructor.length;
baseConstructor.apply(this, args.slice(i, j));
i = j, j = args.length;
extendedConstructor.apply(this, args.slice(i, j));
}
Object.defineProperty(Constructor, 'length', { // fix .length
value: baseConstructor.length + extendedConstructor.length,
configurable: true
});
Constructor.prototype = Object.create(baseConstructor.prototype);
Constructor.prototype.constructor = Constructor;
Object.assign(Constructor.prototype, prototypeLayer);
return Constructor;
}
So then
function Foo(x) {this.foo = x;}
Foo.prototype.fizz = 1;
var Bar = extend(Foo, function (x) {this.bar = x;}, {buzz: 1});
// ...
var b = new Bar('foo', 'bar');
b.foo; // "foo"
b.bar; // "bar"
b instanceof Foo; // true
b instanceof Bar; // true
b.fizz; // 1
b.buzz; // 1
Please note that this is an example of the algorithm you should be following when you write each extended constructor, not production code

Your code would be the following
function TList(){
this.FList = [];
}
TList.prototype.AddElement = function(Ele){
this.FList.push(Ele);
}
TList.prototype.RemoveElement = function(Ele){
this.FList.splice(Ele,1); //Ele is the index to remove;
}
This is an approximation to know how the inherit works in JavaScript.
function TAlertList (){
TList.call(this);
}
TAlertList.prototype = Object.create(TList.prototype);
TAlertList.prototype.constructor = TAlertList;
TAlertList.prototype.AddElement = function(ele){
alert('Element will be added');
TList.prototype.AddElement.call(this,ele);
};
TAlertList.prototype.RemoveElement = function(ele){
alert('Element will be remove');
TList.prototype.RemoveElement.call(this,ele);
};
So, the classic super call is
ParentClass.prototype.myMethod.call(this,args);

This is Q&A
Edit - Don't forget to read #paul's comment too if you planning to read the full text.
Almost all the answers came in were based on the popular "Person" example in the MDN documentation about JS OOP.
The theory behind this method is to put the fields of the object inside a constructor function while implementing the methods in a prototype object. A child object can inherit all the fields by calling the constructor function with a contrived this value. Also it can inherit all the methods by having the same prototype object of the parent as it's prototype object too. The only rule is that you need to call the methods using call or apply to point the methods to the correct this object when implementing inheritance.
I didn't like this approach for two reasons.
The fields and methods of an objects has to be separated between two objects (fields - constructor function, methods - prototype). This doesn't have the flavor of a unique behavior of a unique entity - which should be a single class.
You have to specify the name of the parent object when inheriting. This is not automatic. Let's say object C inherits from the object A. So, inside the methods of the object C, you need to mention object A when inheriting from it. (TList.prototype.AddElement.call(this, Ele);) What if object B comes in between later on? You will have to change all the inheriting methods of C to call from B. This is in no way near good inheritance.
I wanted to overcome these problems in MDN method. I came up with the following model with no this no call and no apply. Code is simple and easy to follow. You don't have to mention the name of the parent object when inheriting from it. So, a new class can come in between the parent and the child at any time without too many changes. Please discuss this and point out the weaknesses of this model.
Here is the function which returns the parent object.
function tList() {
var ret = Object.create(null);
ret.list = [];
ret.addElement = fucntion(ele) {
ret.list.push(ele)
};
return ret;
}
//You can create tList object like this:
var myList = tList();
myList.addElement('foo');
Now comes the child object:
function tAlertList() {
var ret = Object.create(tList());
//Lets inherit with the fashion of overriding a virtual method
ret.addElement = function(ele) {
//Here is new code
alert('Adding element ' + ele);
//Automatic inheritance now
Object.getPrototypeOf(ret).addElement(ele);
}
return ret;
}
//Just create the child object and use it
var myAlertList = tAlertList();
myAlertList.addElement('buzz') ;
You can have grand children object and inherit from parent without mentioning their names. Let's say you have to put tCustomList between tList and tAlertList. All you have to do is to tell the tAlertList to inherit from tCustomList in a single place. (var ret = Object.create(tCustomList());) Everything else remain the same.
Here is the fiddle.

With pure ES5, you could do it like this:
function TList() {
this.FList = []; //not really ideal.
}
TList.prototype.addElement = function(ele) {
this.FList.push(ele);
};
TList.prototype.removeElement = function(ele) {
this.FList.splice(this.FList.indexOf(ele), 1);
}
function TAlertList(){
this.FList = [];
}
TAlertList.prototype = new TList(); //inherit from TList
TAlertList.prototype.constructor = TAlertList; //reset constructor
TAlertList.prototype.addElement = function(ele) {
alert('element will be added');
TList.prototype.addElement.call(this, ele);
};
TAlertList.prototype.removeElement = function(ele) {
alert('element removed');
TList.prototype.removeElement.call(this, ele);
};
Couple of notes:
The FList property of its parent will actually be shared amongst all objects that inherit from the parent unless overwritten. That means that if you don't overwrite FList you'll get this:
var a = new TAlertList();
var b = new TAlertList();
a.push(1); //b.Flist === [1]
In my opinion, it would be best if you named your children functions with other names different from the parent. This way you don't need to do:
TList.prototype.function.call(this, parameter1, parameter2, ..);
You can just call them like this:
this.function(paremeter1, parameter2);
Of course, it's not a static way to call the parent as you can overwrite the function with your own. Then again TList.prototype.function isn't necessary the function of the parent of the object that owns the function. For that you'd need to use non-standard ES5 __proto__ property.
this.__proto__.function.call(this, parameter1, parameter2, ..);
Unless you plan on juggling the function around different objects, you don't need that.

How do I augment a method from the superclass in javascript

I have a method in a base class that I want to keep in a subclass, but just add to it. I've found lots of stuff on augmenting classes and objects with properties and methods, but I can't find, or don't understand, how to just augment the method. The worst case scenario is that I would have to paste the entire method of the parent class into the subclass, but that seems like duplicate code... please help
function someObject (){
this.someProperty = 1;
this.incrementProperty = function incrementProperty(){
this.propertyOfSomeObject += 1;
}
}
function newObject (){
someObject.call(this);
this.incrementProperty = function incrementProperty(){
//do everything the super class has for this property already
return this.someProperty;
}
}
var incrementer = new newObject;
alert (incrementer.incrementProperty()); //I want output to be 2

// parent object
function someObject () {
this.someProperty = 1;
}
// add incrementProperty to the prototype so you're not creating a new function
// every time you instantiate the object
someObject.prototype.incrementProperty = function() {
this.someProperty += 1;
return this.someProperty;
}
// child object
function newObject () {
// we could do useful work here
}
// setup new object as a child class of someObject
newObject.prototype = new someObject();
// this allows us to use "parent" to call someObject's functions
newObject.prototype.parent = someObject.prototype;
// make sure the constructor points to the right place (not someObject)
newObject.constructor = newObject;
newObject.prototype.incrementProperty = function() {
// do everything the super class has for this property already
this.parent.incrementProperty.call(this);
return this.someProperty;
}
var incrementer = new newObject();
alert (incrementer.incrementProperty()); // I want output to be 2
See: http://jsfiddle.net/J7RhA/

this should do, you have to use prototype to have a real concept of oo with javascript
function someObject (){
this.someProperty = 1;
this.propertyOfSomeObject = 0;
this.incrementProperty = function incrementProperty(){
this.propertyOfSomeObject += 1;
return this.propertyOfSomeObject;
}
}
function newObject (){
someObject.call(this);
this.incrementProperty = function incrementProperty(){
this.__super__.incrementProperty.apply(this);
return this.propertyOfSomeObject + 1;
}
}
newObject.prototype = new someObject()
newObject.prototype.__super__ = newObject.prototype
var incrementer = new newObject();
alert(incrementer.incrementProperty()); //I want output to be 2
experiment removing incrementProperty from newObject and it will return 1

I usually use the augment library to write classes in JavaScript. This is how I would rewrite your code using augment:
var Foo = Object.augment(function () {
this.constructor = function () {
this.someProperty = 1;
};
this.incrementProperty = function () {
this.someProperty++;
};
});
var Bar = Foo.augment(function (base) {
this.constructor = function () {
base.constructor.call(this);
};
this.incrementProperty = function () {
base.incrementProperty.call(this);
return this.someProperty;
};
});
As you can see since Bar extends Foo it gets Foo.prototype as a parameter (which we call base). This allows you to easily call the base class constructor and incrementProperty functions. It also shows that the constructor itself is just another method defined on the prototype.
var bar = new Bar;
alert(bar.incrementProperty());
The output will be 2 as expected. See the demo for yourself: http://jsfiddle.net/47gmQ/

From this answer:
Overriding functions
Sometimes children need to extend parent functions.
You want the 'child' (=RussionMini) to do something extra. When RussionMini can call the Hamster code to do something and then do something extra you don't need to copy and paste Hamster code to RussionMini.
In the following example we assume that a Hamster can run 3km an hour but a Russion mini can only run half as fast. We can hard code 3/2 in RussionMini but if this value were to change we have multiple places in code where it needs changing. Here is how we use Hamster.prototype to get the parent (Hamster) speed.
// from goog.inherits in closure library
var inherits = function(childCtor, parentCtor) {
function tempCtor() {};
tempCtor.prototype = parentCtor.prototype;
childCtor.prototype = new tempCtor();
childCtor.prototype.constructor = childCtor;
};
var Hamster = function(name){
if(name===undefined){
throw new Error("Name cannot be undefined");
}
this.name=name;
}
Hamster.prototype.getSpeed=function(){
return 3;
}
Hamster.prototype.run=function(){
//Russionmini does not need to implement this function as
//it will do exactly the same as it does for Hamster
//But Russionmini does need to implement getSpeed as it
//won't return the same as Hamster (see later in the code)
return "I am running at " +
this.getSpeed() + "km an hour.";
}
var RussionMini=function(name){
Hamster.apply(this,arguments);
}
//call this before setting RussionMini prototypes
inherits(RussionMini,Hamster);
RussionMini.prototype.getSpeed=function(){
return Hamster.prototype
.getSpeed.call(this)/2;
}
var betty=new RussionMini("Betty");
console.log(betty.run());//=I am running at 1.5km an hour.

javascript inheritance pattern confusion

I find this is most recommended way to do inheritance in javascript.
function extend(Child, Parent) {
var F = function(){};
F.prototype = Parent.prototype;
Child.prototype = new F();
}
what if I already have methods in child's prototype, aren't they will overwrite, shouldn't we preserve them.
function extend(Child, Parent) {
var c = child.prototype;
var oldProto = new C();
var F = function(){};
F.prototype = Parent.prototype;
Child.prototype = new F();
for(var i in oldProto ){
Child.prototype[i] = oldProto[i]
}
}

I'm not sure if this is any good to you, but it's well important to remember: prototypes are not the same things as classes. What you're doing is trying to make JS behave like a traditional OO language, which is trying to teach a dolphin to dance ballet, or forcing a tiger to become vegan: Admirable, but destined to end in tears.
I can't really see why you'd want to use the extend function to do whatever it is you're trying to do. Why not simply use this:
function Parent()
{};
function Child()
{};
//augment parent proto
Parent.prototype.parentMethod1 = function()
{};
//set Child's proto to Parent
Child.prototype = new Parent();
Child.prototype.constructor = Child;
//Then augment the Child's prototype
Child.prototype.childMethod1 = function()
{};
var foo = new Child();
foo.parentMethod1();//works
foo.childMethod1();//works, too
IMO, this solves the problem entirely. Sure, it's a tad more verbose, but OOP always is.

The pattern you're trying to achieve is called multiple inheritance. And it's highly not recommended for the use because of the issue you're experiencing, called diamond problem. Just use mixin pattern instead.

The code below is the one of the best I have seen for doing inheritance in JavaScript.
Object.create(proto [, propertiesObject ]) is discussed on MDN here.
Below, Jon defines a base empty object called ExtendBase then adds a function property called extend which is not enumerable which takes as its argument a single new object.
That object should contain enumerable properties such as methods and data that will be added to the base object.
He gets all the enumerable properties from the passed object, then creates an array of the necessary descriptors to pass into Object.create using those properties' names. He then uses the parent object as the prototype and resultant descriptors as new properties to be added to the child object directly in the Object.create() call.
As you can see, you can use an object argument with properties, including methods, to extend a parent without losing that passed object's properties with the result being a child object with the parent as the prototype and the enumerable objects of the passed object added directly to the child.
However, this maintains a clean prototype chain while intending to extend parent objects using other objects which are created sanely to extend the parent into a new child in a way that makes sense:
Live sample here (Press F12 in Chrome for console output, or use FireBug in FireFox, etc.)
JavaScript:
// Original Author: FireFly - Jonas Höglund - ##javascript channel
// on irc.freenode.net - see THANKS File. Updated to private data
// members and passable initial parameters by Scott Sanbar
///////////////
// Library code
///////////////
var ExtendBase = {};
Object.defineProperty(ExtendBase, 'extend', {
enumerable:false, value:function (obj) {
'use strict';
var descs = {};
Object.getOwnPropertyNames(obj).forEach(function (key) {
descs[key] = Object.getOwnPropertyDescriptor(obj, key)
});
return Object.create(this, descs);
}
});
///////////////
// Sample Usage
///////////////
function PersonObj(nam) {
return {
name:new function () {
var name = nam;
this.set = function (value) {
name = value;
};
this.get = function () {
return name;
}
},
// A person can tell you its name.
talk:function () {
return "Hello, I'm " + this.name.get();
}
}
}
;
function WorkingPersonObj(occ) {
return {
occupation:new function () {
var occupation = occ;
this.set = function (value) {
occupation = value;
};
this.get = function () {
return occupation;
}
},
// A working person also tells you their occupation when they talk.
talk:function () {
return Person.talk.call(this) + " and I am a " + this.occupation.get();
}
}
}
;
var hush = {
hush:function () {
return "I am supposed to be quiet";
}
};
var Person = ExtendBase.extend(new PersonObj('Harry'));
var WorkingPerson = Person.extend(new WorkingPersonObj('wizard'));
var wp1 = WorkingPerson.extend(hush);
console.log(wp1.talk()); // "Hello, I'm Harry and I am a wizard"
console.log(wp1.hush()); // "I am supposed to be quiet"
wp1.name.set("Elijah");
wp1.occupation.set("prophet");
console.log(wp1.talk()); // "Hello, I'm Elijah and I am a prophet"
console.log(wp1.name.get());
console.log(wp1.occupation.get());

javascript inheritance with protected variables

Is it possible in javascript to have a variable that is not able to access out side the class's functions, but is able to be accessed by classes that inherit it? I.E:
class1 has protected var x = 4;
class2 inherits class1;
class2.prototype.getVar = function(){return /* parent, uber, super, whatever */ this.x;};
var cl2 = new class2();
console.log(cl2.x) // undefined
console.log(cl2.getVar()) // 4

No. Prototypal inheritance is limited to properties of objects.
Variables within the constructor are only available to other code in that variable scope.
You could probably come up with something like...
function cls1() {
var a = 'foo';
this.some_func = function() {
alert(a);
};
}
function cls2() {
cls1.apply(this, arguments);
var cls1_func = this.some_func;
var b = 'bar'
this.some_func = function() {
cls1_func.apply(this, arguments);
alert(b);
};
}
var x = new cls2;
x.some_func(); // alert "foo" alert "bar"
Or to make it more specific to your pseudo code...
function class1() {
var x = 4;
this.getVar = function() {
return x;
};
}
function class2() {
class1.apply(this, arguments);
var cls1_get_var = this.getVar;
this.getVar = function() {
return cls1_get_var.apply(this, arguments);
};
}
class2.prototype = Object.create( class1.prototype );
var cl2 = new class2;
console.log(cl2.x) // undefined
console.log(cl2.getVar()) // 4

I think you need to use a closure to achieve what your trying to do. Something like this:
Class1 = function() {
var x = 4;
return {
getVar: function() {
return x;
}
}
} ();// executes the function immediately and returns an
//an object with one method - getVar. Through closure this method
//still has access to the variable x
Class2 = function() { };// define a constructor function
Class2.prototype = Class1;//have it inherit from Class1
Cl2 = new Class2();//instantiate a new instance of Class2
console.log(Cl2.x);//this is undefined
console.log(Cl2.getVar());//this outputs 4
This is one of the neat things about javascript in that you can achieve the same things in javascript as you would in a class based language without all the extra key words. Douglas Crockford (always good to consult about javascript) explains prototypal inheritance here
Edit:
Just had a second look at your question.If you want newly created methods in your class to access the variable in the base class then you would have to call the getVar method within your own method.Like such:
Class2 = function() {
this.getVar2 = function() {
return this.getVar();
}
};
console.log(Cl2.getVar2()) //outputs 4

Dynamically creating a new javascript class from an existing object

Say I have the following code:
var album = new MyObject('album');
Assume that when the object is constructed, a bunch of properties relative to only albums are loaded via AJAX. Would it be possible to create an Album class so that at a later point, I may just do this:
var anotherAlbum = new Album();
The Album constructor would automatically set the properties that are unique to album objects, based on what was loaded when creating MyObject('album')

JavaScript is prototypal, not classical, so if you think in terms of classes, you're doing it wrong.
You don't have to use the new operator at all. You can create a new object using the object literal:
var myObject = {attr1: 'val1', attr2: 'val2'};
Then you can create a new instance of that object:
var mySecondObject = Object.create(myObject);
Now you can change the attributes of mySecondObject, and if it has methods you can overload them just as easily:
mySecondObject.attr1 = "Hello";
mySecondObject.attr2 = function() {
return "World!";
};
And then mySecondObject will of course have all the properties that you gave myObject at creation.
Be aware that this is a simple version, and that this leaves all attributes 'public'. If you need some privacy, it can be achieved by adding some functions to the mix. It's a bit more complicated though, so let me know if you're interested...

JavaScript "classes", just like any other object, can be dynamically created. So, yes, this can be done.
You would do something like this in the code handling the AJAX response (assuming that the AJAX response was providing the name of the new "class", and it's in a variable called newClassName):
window[newClassName] = function() {
// New class name constructor code
}
window[newClassName].prototype = {
someProperty: "someValue",
someMethod: function(a, b) {
},
someOtherMethod: function(x) {
}
}

This is actually the only for of inheritance that JavaScript has. JavaScript has prototypal inheritance (which can be used to recreate classical inheritance). That means that inheritance is from another object, not a class definition.
To create an object that has all the properties of another object is simple:
function Album() {
// do whatever initialization you need to here, all the properties of album
// are available on 'this'
// e.g.,
doSomething(this.albumName);
}
Album.prototype = album;
var anotherAlbum = new Album();

You can use Douglas Crockford's Functional Inheritance Pattern. Code from Javascript Good Parts book
var mammal = function (spec) {
var that = {};
that.get_name = function ( ) {
return spec.name;
};
that.says = function ( ) {
return spec.saying || '';
};
return that;
};
var myMammal = mammal({name: 'Herb'});
var cat = function (spec) {
spec.saying = spec.saying || 'meow';
var that = mammal(spec);
that.purr = function (n) {
var i, s = '';
for (i = 0; i < n; i += 1) {
if (s) {
s += '-';
}
s += 'r';
}
return s;
};
that.get_name = function ( ) {
return that.says( ) + ' ' + spec.name +
' ' + that.says( );
return that;
};
var myCat = cat({name: 'Henrietta'});
It uses functions to decorate existing javascript objects with new functions and properties. Like this you can add new functions and properties on the fly to your existing object

You can do this
var NewClass=function(){
this.id=null;
this.name=null;
this.show=function(){
alert(this.id+" "+this.name;
}
}
NewClass.prototype.clear=function(){
this.id=null;
this.name=null;
};
...
var ins1=new NewClass();
var ins2=new NewClass();