Related
Why this question is not a duplicate
This answer javascript inheritance from multiple objects does not solve my problem (although it has been marked as a duplicate of my previous question), because it is not scalable as it violates the DRY principle.
For this to work, one would have to manually reference each method like this :
Foo2.prototype.a = function() { /*code...*/};
Foo2.prototype.b = function() { /*code...*/};
Foo2.prototype.c = function() { /*code...*/};
Foo2.prototype.d = function() { /*code...*/};
//and so on and so on...
And what if I have dozens of classes containing dozens of methods ? Should I really manually copy-paste the same reference for each and every class over and over again in my source code ? While this solution would work for a very low number of classes, it is just not usable in a large-scale application using dozens or hundreds of classes.
The problem I'm trying to solve
I'm trying to instantiate objects which must inherit all the properties and methods of Animal and Flying_object using new keyword.
var objA = new Fish(),
objB = new Bird(),
objC = new UFO();
Tricky part is Animal and Flying_object can NOT have a parent-child relationship.
I know JavaScript doesn't implement native methods for multi-inheritance, so I'm posting this question to get some help finding a custom, scalable solution to this problem.
Code example and expected behavior
var Living_being = function() { this.className = 'Living_being'; };
var Animal = function() {
this.className = 'Animal';
this.vector = {x: 0, y: 0};
}
Animal.prototype = new Living_being();
Animal.prototype.getClassName = function() { console.log('Instance of... '+ this.className); };
Animal.prototype.get_vector = function() { console.log(this.vector); }
var Flying_object = function() {
this.className = 'Flying_object';
this.value = 'some value';
}
Flying_object.prototype.getClassName = function() { console.log('Instance of... '+ this.className); };
Flying_object.prototype.get_val = function() { console.log(this.value); }
// So far so good...
var UFO = function() {};
UFO.protoype = new Flying_object(); //classical inheritance
var Fish = function() {};
Fish.protoype = new Animal(); //classical inheritance
// Now the tricky part: how to make Bird share all of the methods and properties of Animal and Flying_object ?
var Bird = function() {};
Bird.prototype = new ....(); //pseudocode where .... is a class containing all the properties of Animal and Flying_object
var instance = new Bird();
//expected result:
instance.getClassName();//--> Instance of...
instance.get_vector(); //--> {x: 0, y: 0}
instance.get_val(); //--> 'some value'
This is where I'm stuck. How can I make Bird inherit from BOTH Animal and Flying_object ?
Any insight would be greatly apprenciated.
Here is a working solution I came up with at some point and gave up because I though there might be a better solution.
#Mörre: I'm not sure this is what you advised me to do in the comments: is this what you called object composition ? Or am I going all wrong here ?
Demo: https://jsfiddle.net/Lau1989/4ba8yrc8/1/
function mix(classA, classB) {
var instanceA = new classA(),
instanceB = new classB();
for (var prop in instanceA) {
instanceB[prop] = instanceA[prop];
}
return instanceB;
}
var Bird = function() { this.className = 'Bird'; };
Bird.prototype = mix(Animal, Flying_object);
var instance = new Bird();
If you need inherit from few classes you can extend prototype Bird from Animal and Ufo using jquery function $.extend({});.
Example $.extend(Bird.prototype,Animal.prototype,UFO.prototype) or you can create custom extend function.If names properties or functions has same names , they will be rewrite.
I got this from documentation: Using Object.assign() extend only enumerable properties.The Object.assign() method only copies enumerable and own properties from a source object to a target object. It uses [[Get]] on the source and [[Set]] on the target, so it will invoke getters and setters. Therefore it assigns properties versus just copying or defining new properties. This may make it unsuitable for merging new properties into a prototype if the merge sources contain getters. For copying property definitions, including their enumerability, into prototypes Object.getOwnPropertyDescriptor() and Object.defineProperty() should be used instead.
JavaScript does not support the concept of multiple inheritance. It also does not implement syntax for mixin and/or trait based composition. But unlike the former, the latter can be achieved by e.g. function and delegation based mixin patterns.
Thus, one first needs to figure out which parts of a composable object system should build the 'is a' relationship and which parts are behavior ('can do' / 'has a') that might get reused by/at different parts/levels of the object system.
The OP already has done this work. The example code that will be provided below is just going to introduce different function based mixin patterns via providing implementations of some behaviors like withLivingBeingBasics and withFlyingAbility ... with the first mixin covering the OP's Living_being class and the second one covering Flying_object.
For better code reuse there are 2 additional mixins, withExposeClassName and withExposeVector that, for the reason of demonstration, compose into the withExposeClassNameAndVector mixin compound.
From this possible base setup, that follows the OP's example, one could continue with shaping the classes.
With the Animal class one is free of choosing where mixin composition shall take place. Following the provided original example, composition at class/prototype level is the better option instead of applying the behavior at construction/instantiation time from within the constructor.
After applying withExposeClassNameAndVector and withLivingBeingBasics to Animal.prototype, any animal instance via prototypal delegation is capable of being invoked at getClassName and getVector as well as at metabolize and reproduce. Thus, at this point, both mixin composition (explicit delegation via call to prototype) and inheritance (automatically running delegation via prototype chain) take place.
The Fish class is implemented easily. As with the OP's example one just follows a simplified inheritance pattern via Fish.prototype = new Animal;. In addition, as already featured with the Animal base class, a class' name gets assigned to its prototype object.
Bird repeats the base patterns of Fish with the exception of featuring its own vector property that now is three dimensional instead of the otherwise prototypal two dimensional one. And since a common bird is supposed to somehow feature flying behavior Bird.prototype has to acquire it from withFlyingAbility.
Following still the OP's example, Ufo also needs to have flying ability. And like a bird, an ufo too has to feature an own three dimensional vector property. Thus the property gets assigned at construction/instantiation time and all the needed behavior gets applied from withExposeClassNameAndVector and from withFlyingAbility to Ufo.prototype.
The provided approach intends to prove that ... the most atomar mixin implements exactly one behavior, ... mixins are not necessarily supposed to introduce state but a behavior might operate upon state, ... mixins can be composed from other mixins, ... they always get applied at object level, either to already existing objects or to the prototype object itself or at composition time from within a constructor function ...
var withLivingBeingBasics = (function () { // function based mixin
function metabolize() { // implement beahvior once.
console.log('every living being features some kind of metabolism.');
}
function reproduce() { // implement beahvior once.
console.log('every living being features some kind of reproduction.');
}
return function() {
this.metabolize = metabolize; // assign shared code.
this.reproduce = reproduce; //
}
}());
var withFlyingAbility = (function () {
function liftOffAerodynamically() {
this.vector.z = 5;
console.log('flying needs some kind of aerodynamic lift.');
}
function monitorAltitudeDifference() {
console.log('monitoring altitude difference : ', this.vector.z);
}
return function() {
this.liftOffAerodynamically = liftOffAerodynamically;
this.monitorAltitudeDifference = monitorAltitudeDifference;
}
}());
var withExposeVector = (function () {
function getVector() {
console.log('vector : ', this.vector);
}
return function() {
this.getVector = getVector;
}
}());
var withExposeClassName = (function () {
function getClassName() {
console.log('Instance of... ', this.className);
}
return function() {
this.getClassName = getClassName;
}
}());
var withExposeClassNameAndVector = function () { // mixin compound.
withExposeClassName.call(this);
withExposeVector.call(this);
}
function Animal() {
//withLivingBeingBasics.call(this); // mixing in for the given example is …
//this.className = 'Animal'; // … better at **class**/prototype level.
this.vector = {x: 0, y: 0};
}
// the many ways of augmenting the `prototype` ...
Object.assign(Animal.prototype, { className: 'Animal' });
//withExposeClassName.call(Animal.prototype);
//withExposeVector.call(Animal.prototype);
withExposeClassNameAndVector.call(Animal.prototype);
withLivingBeingBasics.call(Animal.prototype);
function Fish() {}
Fish.prototype = new Animal;
Object.assign(Fish.prototype, { className: 'Fish' });
function Bird() {
this.vector = {x: 0, y: 0, z: 0};
}
Bird.prototype = new Animal;
Object.assign(Bird.prototype, { className: 'Bird' });
withFlyingAbility.call(Bird.prototype);
function Ufo() {
this.vector = {x: 0, y: 0, z: 0};
}
Object.assign(Ufo.prototype, { className: 'Ufo' });
//withExposeClassName.call(Ufo.prototype);
//withExposeVector.call(Ufo.prototype);
withExposeClassNameAndVector.call(Ufo.prototype);
withFlyingAbility.call(Ufo.prototype);
var fish = new Fish;
var bird = new Bird;
var ufo = new Ufo;
console.log('(fish instanceof Animal) ? ', (fish instanceof Animal));
console.log('(fish instanceof Fish) ? ', (fish instanceof Fish));
fish.getClassName();
fish.metabolize();
fish.reproduce();
fish.getVector();
console.log('(bird instanceof Animal) ? ', (bird instanceof Animal));
console.log('(bird instanceof Bird) ? ', (bird instanceof Bird));
bird.getClassName();
bird.metabolize();
bird.reproduce();
bird.getVector();
bird.monitorAltitudeDifference();
bird.liftOffAerodynamically();
bird.monitorAltitudeDifference();
console.log('(ufo instanceof Ufo) ? ', (ufo instanceof Ufo));
ufo.getClassName();
ufo.getVector();
ufo.monitorAltitudeDifference();
ufo.liftOffAerodynamically();
ufo.monitorAltitudeDifference();
.as-console-wrapper { max-height: 100%!important; top: 0; }
For further reading on SO one might give the following related questions and solutions a chance ...
What are the practical differences between Mixins and Inheritance in Javascript?
Mixins for ES6 classes, transpiled with babel
Traits in javascript
Accessors Composition in ES6 Classes
I have a set of JavaScript "classes" where a base class defines functions that are then shared by an inherited class. It is working, and it is set up like this:
var ThingA = function(name) {
this.name = name;
};
ThingA.prototype = {
sayHi: function() {
alert('Hi, ' + this.name + '!');
}
};
var ThingB = function() {
ThingA.call(this, 'Charlie');
};
ThingB.prototype = new ThingA();
ThingB.prototype.constructor = ThingB;
var instanceOfB = new ThingB();
instanceOfB.sayHi(); // alerts 'Hi, Charlie!'
For reasons that are outside of my control, my company prefers to follow this pattern when writing JavaScript:
SomeClass = function() {
// "Private" functions go here
function somePrivateMethod() {
...
}
return {
// "Public" methods go here
somePublicMethod: function() { ... }
};
}();
Now, this is fine as far as things go, and it works well for many situations. But it is more of a functional style. There is only one "class" instance, and everything is static.
I've been asked to modify my working code to more closely match the style my company prefers. So my question is, there a way to inherit from a class that is wrapped inside a factory class? It would look something like this:
FactoryClassA = function() {
var ThingA = function(name) {
this.name = name;
};
ThingA.prototype = {
sayHi: function() {
alert('Hi, ' + this.name + '!');
}
};
return {
createThingA: function(name) {
return new ThingA(name);
}
};
}();
FactoryClassB = function() {
// Define a ThingB class that inherits from ThingA somehow
return {
createThingB: function() {
return new ThingB();
}
};
}();
var instanceOfB = FactoryClassB.createThingB();
instanceOfB.sayHi(); // should alert 'Hi, Charlie!'
Is there a way to define ThingB wrapped in FactoryClassB that inherits from ThingA wrapped in FactoryClassA? Thanks to this question, I know that I'm not going to be able to do it exactly like this. I am thinking of using a method to extend a given class ... somehow?
This answer seems close, but I'm having trouble figuring out the details of how to modify that example to fit with the specifics of my situation. I am willing to bend my company's usual pattern a little bit, but can I at least get closer to it?
UPDATE 1
In response to Adam's comment to just add a parameter to the factory class, here's where I'm stuck:
ThingB.prototype = new ThingA();
ThingB.prototype.constructor = ThingB;
I can't figure out how to adapt these lines to make it work if I just pass in a parameter to the factory class method.
Below is what (I believe) you're looking for:
FactoryClassA = function() {
var ThingA = function(name) {
this.name = name;
};
ThingA.prototype = {
sayHi: function() {
console.log('Hi, ' + this.name + '!');
}
};
// Add the constructor back to the prototype
// (see explanation below)
ThingA.prototype.constructor = ThingA;
return {
createThingA: function(name) {
return new ThingA(name);
}
};
}();
FactoryClassB = function() {
// Bootstrapping:
// Capture the instance, as we'll need it to set up the prototype
var baseInstance = new FactoryClassA.createThingA();
// Capture the constructor
var baseConstructor = baseInstance.constructor;
// Keep a reference to the base prototype
var baseProto = baseConstructor.prototype;
function ThingB(name) {
// Call base constructor, along with our args
baseConstructor.call(this, name);
};
ThingB.prototype = baseInstance;
ThingB.prototype.constructor = ThingB;
ThingB.prototype.sayHi = function() {
console.log('here I am');
// call the base class `sayHi`
baseProto.sayHi.call(this);
};
return {
createThingB: function(name) {
return new ThingB(name);
}
};
}();
// Testing
var foo = FactoryClassB.createThingB("Indeed");
foo.sayHi();
// Output:
// here I am
// hi indeed
Explanation:
in FactoryClassA, this line is necessary:
ThingA.prototype.constructor = ThingA;
Note that every prototype in JS is automatically created with a reference to its constructor. For example, when you do:
function T(){}
T.prototype already has a property called constructor which points back to T.
However, in your implementation of ThingA, you reset the entire prototype, by doing ThingA.prototype = { ... }. Therefore, you now have lost the reference to its constructor. In 99% of cases it is ok, and won't have any negative side effects (which is probably why most developers tend to forget it). However, in the case of inheritance, it may be necessary.
Now, within FactoryClassB, we need to do some bootstrapping:
var baseInstance = new FactoryClassA.createThingA();
var baseConstructor = baseInstance.constructor;
var baseProto = baseConstructor.prototype;
Observe the last two lines, as they are pivotal to achieving inheritance in this design pattern. First, since ThingA's constructor is accessible via the prototype (ThingA.prototype.constructor = ThingA), then it means that given an instance of ThingA, we can directly retrieve its constructor. Since the constructor is the function itself, and since every function has a reference to its prototype, we can keep a reference of ThingA.prototype with baseConstructor.prototype.
Next is the critical part, where we set up the inheritance chain:
function ThingB(name) {
// Call the base constructor
baseConstructor.call(this, name);
};
ThingB.prototype = baseInstance;
ThingB.prototype.constructor = ThingB;
The last line above is quite important, as it tells the prototype what its constructor is, otherwise it would still point to ThingA.
There you have it - prototypal inheritance.
Side note:
You can probably see how the above can get quite tedious, a little grotesque, and repetitive. Ergo, you might want to consider an inheritance library like Fiber.js which follows the encapsulation pattern you desired (along with some bonuses like mixins and decorators). Disclaimer: I authored the library.
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
Basically I want inheritable functions as in
Base = function() { };
Base.prototype.foo = function() {
console.log("base foo");
};
Derived = function() { };
somelib.inherit(Derived, Base);
Derived.prototype.foo = function() {
console.log("derived foo");
}
d = new Derived():
d.foo();
And I want it to print
derived foo
base foo
Yes I know I can explicitly call Base.prototype.foo.call(this); I'm just wondering if there is a pattern for calling overridden super class functions automatically. The problem I'm trying to solve is 2 fold.
derived classes should NOT have to remember to call their parent's method, it just happens automatically.
if 1. can't happen then at least I'd like Derived not to call Base by name since that's brittle. Rather I'd like it call parentclass or something so you don't have to know the base. That way if you change the name of the base you don't have to go fixing every derived class.
You can implement such functionality by using a structure like:
function Base(){}
Base.prototype.destroy = function(){console.log('Base destroy');};
function Derived(){}
Derived.prototype = new Base; // Let Derived inherit from Base
// Override the `destroy` method
Derived.prototype.destroy = function() {
console.log('Derived destroy');
// Call parent class method
this.constructor.prototype.destroy();
// If the context of the method is important, you can use Function.call:
//this.constructor.prototype.destroy.call(this);
};
// Create an instance of Derived, and call the destroy method:
(new Derived).destroy();
I would suggest thinking about exactly why you are doing this, at least in terms of requirement #1. Keep in mind that your desired pattern would take away a great deal of flexibility. For instance, if you have a situation where you want to print the statements in the opposite order:
base foo
derived foo
You would either have to abandon your pattern or create a function foo2() in the derived class which then calls foo() in the base class. Neither is very pretty.
Same goes if you even want to do something as simple as:
derived foo
base foo
one more thing in the derived function
I would contend that using this pattern may work for the exact thing you want to do right now, but may give you fits when you want to make a seemingly trivial change down the road. All to save one line of code!
As far as I know there is no language integrated destructor functionality in JavaScript. It is all about frameworks. If you are using ASP.NET Ajax, for example, the framework would expect that your objects would have a dispose method, responsible for freeing up resources (event handlers). So, it is up to you.
Ok, this isn't quite what you are looking for, in that it's not a "pattern", but it is a potential implementation path you could follow:
Take a look # the MooTools Class.Extras package (for lack of a better word). Using the Chain Class, you could probably get the desired functionality.
var parent = (function () {
var construct = function () {
};
construct.prototype = {
constructor: construct,
destroy: function () {
console.log('parent destruction');
}
}
return construct;
})();
var child = (function (parent) {
var construct = function () {
};
construct.prototype = Object.create(parent.prototype);
construct.prototype.constructor = construct;
construct.prototype.destroy = function () {
parent.prototype.destroy.call(this); // calling parent, too
console.log('child destruction');
};
return construct;
})(parent);
child_instance = new child();
child_instance.destroy();
I would prefer a way where I don't assign Derived = chainify() so that the api would be the same as you had in your question but as of right now this is the best way I can get it to work. It works by replacing each method of the object with a method that calls the replaced method and travels up the parent chain calling their methods along the way.
function chainify() {
return function () {
var property;
for (property in this) {
if (typeof this[property] === "function") {
this[property] = chain(this[property], property);
}
}
function chain(method, method_name) {
return function() {
method();
var current = this;
while (current = current.parent) {
if (current.hasOwnProperty(method_name)) {
current[method_name].apply(this, arguments);
}
}
};
}
}
}
var somelib = function() { };
somelib.inherit = function (derive, base) {
derive.prototype = new base;
derive.prototype.parent = base.prototype;
};
var Base = function() { };
Base.prototype.foo = function() {
console.log("base foo");
};
var Derived = chainify();
somelib.inherit(Derived, Base);
Derived.prototype.foo = function() {
console.log("derived foo");
};
d = new Derived();
d.foo();
I've put these together with the help of others and several resources. I've made a fiddle of everything, and the stripped down code is posted below.
Basically I've learned how to use each of these patterns but I'm curious about the more fundamental differences between these approaches. Downstream code is practically identical with any of these patterns, but is there a reason why one should use one over another, beyond personal preference? Also though I've tried to gather up the most common patterns, please suggest your own if it's better.
Pattern 1 (Object Based):
var mouseDiff = {
"startPoint" : {"x" :0, "y" : 0},
"hypotenuse" : function(a,b) {
// do something
},
"init" : function(){
// do something
}
}
mouseDiff.init();
Pattern 2 (Most traditional as far as I know):
function MouseDiff() {
this.startPoint = {"x" :0, "y" : 0};
}
MouseDiff.prototype.hypotenuse = function(a,b) {
// do something
}
MouseDiff.prototype.init = function() {
// do something
}
var myMouse = new MouseDiff;
myMouse.init();
Pattern 3 (Making use of closure):
var MouseDiff2 = (function() {
var startPoint = {"x" :0, "y" : 0};
var hypotenuse = function(a,b) {
// do something
};
return {
hypotenuse: hypotenuse,
init : function(){
// do something
}
};
}());
MouseDiff2.init();
Pattern 1 is a singleton. If you only need one such object, it's just fine.
Pattern 2 builds new objects, and takes advantage of the prototype object so that when a new MouseDiff object is created, it will not create new copies of the functions (which are themselves data in JavaScript).
Pattern 3 requires more memory in comparison to a regular singleton but it offers static privacy.
I like the following pattern, as it covers various features, though it is really a combination of the constructor (pattern 2) and closure (pattern 3):
var MouseDiff = (function () {
var aStaticVariable = 'Woohoo!';
// And if you really need 100% truly private instance
// variables which are not methods and which can be
// shared between methods (and don't mind the rather
// big hassle they require), see
// http://brettz9.blogspot.com/search?q=relator
// (see also the new plans for a Map/WeakMap in ECMAScript)
function _APrivateStaticMethod () {
alert(aStaticVariable);
}
// An instance method meant to be called on the
// particular object as via ".call(this)" below
function _APrivateInstanceMethod () {
alert(this.startPoint.x);
}
// Begin Constructor
function MouseDiff() {
this.startPoint = {"x" :0, "y" : 0};
}
MouseDiff.prototype.hypotenuse = function(a,b) {
// do something
};
MouseDiff.prototype.init = function() {
// do something
_APrivateStaticMethod(); // alerts 'Woohoo!'
_APrivateInstanceMethod.call(this); // alerts 0 (but if not
// called with this, _APrivateInstanceMethod's internal
// "this" will refer (potentially dangerously) to the
// global object, as in the window in the browser unless
// this class was defined within 'strict' mode in which
// case "this" would be undefined)
};
return MouseDiff;
}());
var myMouse = new MouseDiff;
myMouse.init();
I do not know enough about JavaScript to tell you what if any performance differences exist between these approaches. Here are just two differences between these I noticed. I'm sure there are others.
Pattern 1 creates one object with those properties, including attached methods. Pattern 2 allows us to easily create many objects with the same methods attached, without rewriting them.
Pattern 3 is like a factory. Instead of relying on prototype to automatically attach these methods, the factory just creates them anew and returns the object. The usage of a closure allows us to hide the "member variables" of the object. There is no way to access startPoint or hypotenuse() except through the "public" interface returned.
Whenever I answer these types of theoretical JavaScript questions, I always fear there is some technical detail I am forgetting or overlooking. If so, let me know, and I will fix the answer.
Pattern two is my personally preference because it is the closest to traditional object oriented programming and allows for easy inheritance.
This post by John Resig (the guy behind JQuery) uses that method...
http://ejohn.org/blog/simple-javascript-inheritance/
[edit]
In fact, I don't think methods 1 or 3 have any benefits. 1 is, as someone else said, a singleton and does not allow multiple instances and 3... I don't know where to start with 3.
There is one more possible way to do this.
var MouseDiff = {};
(function(context) {
var privateVarialble = 0;
context.hypotenuse = function() {
//code here
};
context.int = function() {
//code here
}
})(MouseDiff);
Here we simply pass the namespace as an argument to a self-invoking function. The privateVarialble variable is private because it does not get assigned to the context.
We can even set the context to the global object (with a one word change!). Inside brackets (MouseDiff) make it (this). This is a big asset for library vendors – who can wrap their features in a self-invoking function and leave it to the user to decide whether they should be global or not.
http://www.jsoops.net/ is quite good for oop in Js. If provide private, protected, public variable and function, and also Inheritance feature. Example Code:
var ClassA = JsOops(function (pri, pro, pub)
{// pri = private, pro = protected, pub = public
pri.className = "I am A ";
this.init = function (var1)// constructor
{
pri.className += var1;
}
pub.getData = function ()
{
return "ClassA(Top=" + pro.getClassName() + ", This=" + pri.getClassName()
+ ", ID=" + pro.getClassId() + ")";
}
pri.getClassName = function () { return pri.className; }
pro.getClassName = function () { return pri.className; }
pro.getClassId = function () { return 1; }
});
var newA = new ClassA("Class");
//***Access public function
console.log(typeof (newA.getData));
// function
console.log(newA.getData());
// ClassA(Top=I am A Class, This=I am A Class, ID=1)
//***You can not access constructor, private and protected function
console.log(typeof (newA.init)); // undefined
console.log(typeof (newA.className)); // undefined
console.log(typeof (newA.pro)); // undefined
console.log(typeof (newA.getClassName)); // undefined
This has been answered elsewhere many times before but just to offer up some variety. ds.oop is a nice way to declare classes with constructors in javascript. It supports every possible type of inheritance (Including 1 type that even c# does not support) as well as Interfaces which is nice.
var Color = ds.make.class({
type: 'Color',
constructor: function (r,g,b) {
this.r = r; /* now r,g, and b are available to */
this.g = g; /* other methods in the Color class */
this.b = b;
}
});
var red = new Color(255,0,0); // using the new keyword to instantiate the class