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How to create converting constructor in javascript? [duplicate]

I prefer to use OOP in large scale projects like the one I'm working on right now. I need to create several classes in JavaScript but, if I'm not mistaken, there are at least a couple of ways to go about doing that. What would be the syntax and why would it be done in that way?
I would like to avoid using third-party libraries - at least at first.
Looking for other answers, I found the article Object-Oriented Programming with JavaScript, Part I: Inheritance - Doc JavaScript that discusses object-oriented programming in JavaScript. Is there a better way to do inheritance?

Here's the way to do it without using any external libraries:
// Define a class like this
function Person(name, gender){
// Add object properties like this
this.name = name;
this.gender = gender;
}
// Add methods like this. All Person objects will be able to invoke this
Person.prototype.speak = function(){
alert("Howdy, my name is" + this.name);
};
// Instantiate new objects with 'new'
var person = new Person("Bob", "M");
// Invoke methods like this
person.speak(); // alerts "Howdy, my name is Bob"
Now the real answer is a whole lot more complex than that. For instance, there is no such thing as classes in JavaScript. JavaScript uses a prototype-based inheritance scheme.
In addition, there are numerous popular JavaScript libraries that have their own style of approximating class-like functionality in JavaScript. You'll want to check out at least Prototype and jQuery.
Deciding which of these is the "best" is a great way to start a holy war on Stack Overflow. If you're embarking on a larger JavaScript-heavy project, it's definitely worth learning a popular library and doing it their way. I'm a Prototype guy, but Stack Overflow seems to lean towards jQuery.
As far as there being only "one way to do it", without any dependencies on external libraries, the way I wrote is pretty much it.

The best way to define a class in JavaScript is to not define a class.
Seriously.
There are several different flavors of object-orientation, some of them are:
class-based OO (first introduced by Smalltalk)
prototype-based OO (first introduced by Self)
multimethod-based OO (first introduced by CommonLoops, I think)
predicate-based OO (no idea)
And probably others I don't know about.
JavaScript implements prototype-based OO. In prototype-based OO, new objects are created by copying other objects (instead of being instantiated from a class template) and methods live directly in objects instead of in classes. Inheritance is done via delegation: if an object doesn't have a method or property, it is looked up on its prototype(s) (i.e. the object it was cloned from), then the prototype's prototypes and so on.
In other words: there are no classes.
JavaScript actually has a nice tweak of that model: constructors. Not only can you create objects by copying existing ones, you can also construct them "out of thin air", so to speak. If you call a function with the new keyword, that function becomes a constructor and the this keyword will not point to the current object but instead to a newly created "empty" one. So, you can configure an object any way you like. In that way, JavaScript constructors can take on one of the roles of classes in traditional class-based OO: serving as a template or blueprint for new objects.
Now, JavaScript is a very powerful language, so it is quite easy to implement a class-based OO system within JavaScript if you want to. However, you should only do this if you really have a need for it and not just because that's the way Java does it.

ES2015 Classes
In the ES2015 specification, you can use the class syntax which is just sugar over the prototype system.
class Person {
constructor(name) {
this.name = name;
}
toString() {
return `My name is ${ this.name }.`;
}
}
class Employee extends Person {
constructor(name, hours) {
super(name);
this.hours = hours;
}
toString() {
return `${ super.toString() } I work ${ this.hours } hours.`;
}
}
Benefits
The main benefit is that static analysis tools find it easier to target this syntax. It is also easier for others coming from class-based languages to use the language as a polyglot.
Caveats
Be wary of its current limitations. To achieve private properties, one must resort to using Symbols or WeakMaps. In future releases, classes will most likely be expanded to include these missing features.
Support
Browser support isn't very good at the moment (supported by nearly everyone except IE), but you can use these features now with a transpiler like Babel.
Resources
Classes in ECMAScript 6 (final semantics)
What? Wait. Really? Oh no! (a post about ES6 classes and privacy)
Compatibility Table – Classes
Babel – Classes

I prefer to use Daniel X. Moore's {SUPER: SYSTEM}. This is a discipline that provides benefits such as true instance variables, trait based inheritance, class hierarchies and configuration options. The example below illustrates the use of true instance variables, which I believe is the biggest advantage. If you don't need instance variables and are happy with only public or private variables then there are probably simpler systems.
function Person(I) {
I = I || {};
Object.reverseMerge(I, {
name: "McLovin",
age: 25,
homeState: "Hawaii"
});
return {
introduce: function() {
return "Hi I'm " + I.name + " and I'm " + I.age;
}
};
}
var fogel = Person({
age: "old enough"
});
fogel.introduce(); // "Hi I'm McLovin and I'm old enough"
Wow, that's not really very useful on it's own, but take a look at adding a subclass:
function Ninja(I) {
I = I || {};
Object.reverseMerge(I, {
belt: "black"
});
// Ninja is a subclass of person
return Object.extend(Person(I), {
greetChallenger: function() {
return "In all my " + I.age + " years as a ninja, I've never met a challenger as worthy as you...";
}
});
}
var resig = Ninja({name: "John Resig"});
resig.introduce(); // "Hi I'm John Resig and I'm 25"
Another advantage is the ability to have modules and trait based inheritance.
// The Bindable module
function Bindable() {
var eventCallbacks = {};
return {
bind: function(event, callback) {
eventCallbacks[event] = eventCallbacks[event] || [];
eventCallbacks[event].push(callback);
},
trigger: function(event) {
var callbacks = eventCallbacks[event];
if(callbacks && callbacks.length) {
var self = this;
callbacks.forEach(function(callback) {
callback(self);
});
}
},
};
}
An example of having the person class include the bindable module.
function Person(I) {
I = I || {};
Object.reverseMerge(I, {
name: "McLovin",
age: 25,
homeState: "Hawaii"
});
var self = {
introduce: function() {
return "Hi I'm " + I.name + " and I'm " + I.age;
}
};
// Including the Bindable module
Object.extend(self, Bindable());
return self;
}
var person = Person();
person.bind("eat", function() {
alert(person.introduce() + " and I'm eating!");
});
person.trigger("eat"); // Blasts the alert!
Disclosure: I am Daniel X. Moore and this is my {SUPER: SYSTEM}. It is the best way to define a class in JavaScript.

var Animal = function(options) {
var name = options.name;
var animal = {};
animal.getName = function() {
return name;
};
var somePrivateMethod = function() {
};
return animal;
};
// usage
var cat = Animal({name: 'tiger'});

Following are the ways to create objects in javascript, which I've used so far
Example 1:
obj = new Object();
obj.name = 'test';
obj.sayHello = function() {
console.log('Hello '+ this.name);
}
Example 2:
obj = {};
obj.name = 'test';
obj.sayHello = function() {
console.log('Hello '+ this.name);
}
obj.sayHello();
Example 3:
var obj = function(nameParam) {
this.name = nameParam;
}
obj.prototype.sayHello = function() {
console.log('Hello '+ this.name);
}
Example 4: Actual benefits of Object.create(). please refer [this link]
var Obj = {
init: function(nameParam) {
this.name = nameParam;
},
sayHello: function() {
console.log('Hello '+ this.name);
}
};
var usrObj = Object.create(Obj); // <== one level of inheritance
usrObj.init('Bob');
usrObj.sayHello();
Example 5 (customised Crockford's Object.create):
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()
}
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();
To keep answer updated with ES6/ ES2015
A class is defined like this:
class Person {
constructor(strName, numAge) {
this.name = strName;
this.age = numAge;
}
toString() {
return '((Class::Person) named ' + this.name + ' & of age ' + this.age + ')';
}
}
let objPerson = new Person("Bob",33);
console.log(objPerson.toString());

I think you should read Douglas Crockford's Prototypal Inheritance in JavaScript and Classical Inheritance in JavaScript.
Examples from his page:
Function.prototype.method = function (name, func) {
this.prototype[name] = func;
return this;
};
Effect? It will allow you to add methods in more elegant way:
function Parenizor(value) {
this.setValue(value);
}
Parenizor.method('setValue', function (value) {
this.value = value;
return this;
});
I also recommend his videos:
Advanced JavaScript.
You can find more videos on his page: http://javascript.crockford.com/
In John Reisig book you can find many examples from Douglas Crockfor's website.

Because I will not admit the YUI/Crockford factory plan and because I like to keep things self contained and extensible this is my variation:
function Person(params)
{
this.name = params.name || defaultnamevalue;
this.role = params.role || defaultrolevalue;
if(typeof(this.speak)=='undefined') //guarantees one time prototyping
{
Person.prototype.speak = function() {/* do whatever */};
}
}
var Robert = new Person({name:'Bob'});
where ideally the typeof test is on something like the first method prototyped

If you're going for simple, you can avoid the "new" keyword entirely and just use factory methods. I prefer this, sometimes, because I like using JSON to create objects.
function getSomeObj(var1, var2){
var obj = {
instancevar1: var1,
instancevar2: var2,
someMethod: function(param)
{
//stuff;
}
};
return obj;
}
var myobj = getSomeObj("var1", "var2");
myobj.someMethod("bla");
I'm not sure what the performance hit is for large objects, though.

var Student = (function () {
function Student(firstname, lastname) {
this.firstname = firstname;
this.lastname = lastname;
this.fullname = firstname + " " + lastname;
}
Student.prototype.sayMyName = function () {
return this.fullname;
};
return Student;
}());
var user = new Student("Jane", "User");
var user_fullname = user.sayMyName();
Thats the way TypeScript compiles class with constructor to JavaScript.

The simple way is:
function Foo(a) {
var that=this;
function privateMethod() { .. }
// public methods
that.add = function(b) {
return a + b;
};
that.avg = function(b) {
return that.add(b) / 2; // calling another public method
};
}
var x = new Foo(10);
alert(x.add(2)); // 12
alert(x.avg(20)); // 15
The reason for that is that this can be bound to something else if you give a method as an event handler, so you save the value during instantiation and use it later.
Edit: it's definitely not the best way, just a simple way. I'm waiting for good answers too!

You probably want to create a type by using the Folding Pattern:
// Here is the constructor section.
var myType = function () {
var N = {}, // Enclosed (private) members are here.
X = this; // Exposed (public) members are here.
(function ENCLOSED_FIELDS() {
N.toggle = false;
N.text = '';
}());
(function EXPOSED_FIELDS() {
X.count = 0;
X.numbers = [1, 2, 3];
}());
// The properties below have access to the enclosed fields.
// Careful with functions exposed within the closure of the
// constructor, each new instance will have it's own copy.
(function EXPOSED_PROPERTIES_WITHIN_CONSTRUCTOR() {
Object.defineProperty(X, 'toggle', {
get: function () {
var before = N.toggle;
N.toggle = !N.toggle;
return before;
}
});
Object.defineProperty(X, 'text', {
get: function () {
return N.text;
},
set: function (value) {
N.text = value;
}
});
}());
};
// Here is the prototype section.
(function PROTOTYPE() {
var P = myType.prototype;
(function EXPOSED_PROPERTIES_WITHIN_PROTOTYPE() {
Object.defineProperty(P, 'numberLength', {
get: function () {
return this.numbers.length;
}
});
}());
(function EXPOSED_METHODS() {
P.incrementNumbersByCount = function () {
var i;
for (i = 0; i < this.numbers.length; i++) {
this.numbers[i] += this.count;
}
};
P.tweak = function () {
if (this.toggle) {
this.count++;
}
this.text = 'tweaked';
};
}());
}());
That code will give you a type called myType. It will have internal private fields called toggle and text. It will also have these exposed members: the fields count and numbers; the properties toggle, text and numberLength; the methods incrementNumbersByCount and tweak.
The Folding Pattern is fully detailed here:
Javascript Folding Pattern

Code golf for #liammclennan's answer.
var Animal = function (args) {
return {
name: args.name,
getName: function () {
return this.name; // member access
},
callGetName: function () {
return this.getName(); // method call
}
};
};
var cat = Animal({ name: 'tiger' });
console.log(cat.callGetName());

MooTools (My Object Oriented Tools) is centered on the idea of classes. You can even extend and implement with inheritance.
When mastered, it makes for ridiculously reusable, powerful javascript.

Object Based Classes with Inheritence
var baseObject =
{
// Replication / Constructor function
new : function(){
return Object.create(this);
},
aProperty : null,
aMethod : function(param){
alert("Heres your " + param + "!");
},
}
newObject = baseObject.new();
newObject.aProperty = "Hello";
anotherObject = Object.create(baseObject);
anotherObject.aProperty = "There";
console.log(newObject.aProperty) // "Hello"
console.log(anotherObject.aProperty) // "There"
console.log(baseObject.aProperty) // null
Simple, sweet, and gets 'er done.

Based on the example of Triptych, this might even be simpler:
// Define a class and instantiate it
var ThePerson = new function Person(name, gender) {
// Add class data members
this.name = name;
this.gender = gender;
// Add class methods
this.hello = function () { alert('Hello, this is ' + this.name); }
}("Bob", "M"); // this instantiates the 'new' object
// Use the object
ThePerson.hello(); // alerts "Hello, this is Bob"
This only creates a single object instance, but is still useful if you want to encapsulate a bunch of names for variable and methods in a class. Normally there would not be the "Bob, M" arguments to the constructor, for example if the methods would be calls to a system with its own data, such as a database or network.
I am still too new with JS to see why this does not use the prototype thing.

A base
function Base(kind) {
this.kind = kind;
}
A class
// Shared var
var _greeting;
(function _init() {
Class.prototype = new Base();
Class.prototype.constructor = Class;
Class.prototype.log = function() { _log.apply(this, arguments); }
_greeting = "Good afternoon!";
})();
function Class(name, kind) {
Base.call(this, kind);
this.name = name;
}
// Shared function
function _log() {
console.log(_greeting + " Me name is " + this.name + " and I'm a " + this.kind);
}
Action
var c = new Class("Joe", "Object");
c.log(); // "Good afternoon! Me name is Joe and I'm a Object"

JavaScript is object-oriented, but it's radically different than other OOP languages like Java, C# or C++. Don't try to understand it like that. Throw that old knowledge out and start anew. JavaScript needs a different thinking.
I'd suggest to get a good manual or something on the subject. I myself found ExtJS Tutorials the best for me, although I haven't used the framework before or after reading it. But it does give a good explanation about what is what in JavaScript world. Sorry, it seems that that content has been removed. Here's a link to archive.org copy instead. Works today. :P

//new way using this and new
function Persons(name) {
this.name = name;
this.greeting = function() {
alert('Hi! I\'m ' + this.name + '.');
};
}
var gee=new Persons("gee");
gee.greeting();
var gray=new Persons("gray");
gray.greeting();
//old way
function createPerson(name){
var obj={};
obj.name=name;
obj.greeting = function(){
console.log("hello I am"+obj.name);
};
return obj;
}
var gita=createPerson('Gita');
gita.greeting();

Best way to call a function in javascript [closed]

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I'm writing a small example to call function getAge() to display age via an object.
I've 3 ways to do that:
"use strict";
var personClass = class {
static getAge() {
return 18
}
};
var personJSON = {
getAge: function () {
return 18
}
};
function personFunc() {
var getAge = function () {
return 18
};
// set a flag to point to getAge function
this.getAge = getAge()
}
$('#btn1').click(function () {
alert(personClass.getAge())
});
$('#btn2').click(function () {
alert(personJSON.getAge())
});
$('#btn3').click(function () {
var p = new personFunc();
alert(p.getAge)
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="btn1">Get age via class</button>
<button id="btn2">Get age via json</button>
<button id="btn3">Get age via function</button>
My question: What's the best way? And why?

It depends on the actual problem you have to solve and the style of programming you're using. If you tend to use an object oriented approach and want to benfit from it's features like inheritance you might want to model a person as
function Person(){
var age = 18;
this.getAge = function() {
return age;
}
}
var person = new Person();
alert(p.getAge());
Or as a class
class Person {
constructor() {
this.age = 18;
}
getAge() {
return this.age()
}
}
If you prefer a more functional style, you'll write pure and independent functions that perform some action on some data:
// does not make much sense in this age of a person context
function age(obj, dateFn) {
return dateFn() - obj.born;
}
var person = { born : new Date(/* */) }
var animal = { born : new Date(/* */) }
alert(age(person, Date.now));
alert(age(animal, Date.UTC));
For the example of getAge, any kind of static function does not make any sense (your first example), since age is the property of some object. So you'll need an instance of an object which you can use to call a method, or to pass to a function.

I would recommend the most simple form:
var personJSON = {
getAge: function () {
return 18;
}
};
It already creates a well-defined object with the desired properties, it scales well and it is not encumbered by red-tape boilerplate code.
Good code already did so for years and it is a very well proven style. It is readable and compact.
What you will NOT get from this are the new advanced features of ES6 class definitions which might be required in more advanced cases.
Warning! This is just my personal, biased opinion:
I, for one, will not use class definitions at all, instead I will leverage this style and lambdas, as I've always done in 10+ years. I'm also contrary to the introduction of syntactical sugar in Javascript just to let it look like other languages. I prefer the prototypical paradigm.

I'm just saying how I would use the three. This is not meant to be an absolute answer, this is the way I see things. And I'm interested to see other people points of view on this.
class
I'd only use this key word in case I want to instantiate multiple times this object. (Only available in ECMAScript 6)
"use strict"
class Animal {
constructor(name) {
this.name = name;
}
speak() {
console.log(this.name + ' makes a noise.');
}
}
class Dog extends Animal {
speak() {
console.log(this.name + ' barks.');
}
}
var bobby = new Dog("Bobby");
bobby.speak();
JSON
I'd only declare a JSON when I'm only going to instantiate it once.
var Game = {
run: function() {
//...
},
stop: function() {
//...
},
pause: function() {
//...
},
maxPlayer: 4,
rooms: [{
roomName: "Room1",
playerNames: ["Player1", "Player2"]
}, {
roomName: "Room2",
playerNames: ["Player1", "Player2", "Player3"]
}]
};
function
You're using it more like a class substitute here. By using new keyword you can instantiate this function as a class as many times as you want. (Which a lot a people do and that's ok ! Mostly because the keyword class is only available in ECMAScript 6)
var Person = function (firstName) {
this.firstName = firstName;
};
Person.prototype.sayHello = function() {
console.log("Hello, I'm " + this.firstName);
};
var person1 = new Person("Alice");
person1.sayHello();

I would suggest something like this. I'd be curious to hear other people's feedback.
//Convention says use capital case if declaring a function as a class.
function Person(age){
//Optional: allow the developer to pass in an age when creating the object
//Otherwise default to 18
this.age = age? age: 18; //ternary operator
//function declaration.
this.getAge = function() {
return this.age;
}
}
$('#btn3').click(function () {
var p = new Person();
alert(p.getAge()) //Alert 18
var p2 = new Person(15);
alert(p2.getAge()) //Alert 15
});
My reasoning for this is that this is an objected oriented way of doing it.
The capital case lets you know that this function is intended to be used with a with the new keyword.
Is reusable - you can have multiple, different Person objects, with different ages, without having to declare the methods each time for each one.
Syntax and usage is similar to object oriented languages like Java which one might already be familiar with.

The last way that you wrote is the best
function personFunc() {
var getAge = function () {
return 18
};
// set a flag to point to getAge function
this.getAge = getAge()
}
Buth there is a better one by perfomance, but little complex by writing. It is like TypeScript or Babel compiles it's classes to JavaScript.
function PersonClass() {
this.age = 18;
}
PersonClass.prototype.getAge = function () {
return this.age;
};
usage is the same:
var person = new PersonClass();
person.getAge();
But to write like this by yourself is little time-consuming. So I think that the best thing for now is to use ES6 classes and compile them with TypeScript or Babel.
So, my opinion is the best way to write like this:
class PersonClass {
private age = 18;
getAge() {
return this.age;
}
}

How can I extend a class defined behind a closure in JavaScript?

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.

Nested class in javascript, inheritance of private methods

i'm quite a newbie in javascript, and i'm spending some time trying to create namespaced objects in js.
Now, that's what i'm trying to do:
MainObject = function() {
var privateVariable = "i'm private";
var privateMethod = function() {
// doSomething
}
this.publicMethod = function() {
// doPublicSomething
}
}
MainObject.prototype.nested = function() {
this.publicNestedMethod = function() {
// that's not working at all
this.privateMethod(privateVariable);
}
}
MyObject = new MainObject();
MyObject.publicMethod();
MyObject.publicNestedMethod();
I tried to include the nested class inside the first one, but it's not working also if i try:
this.nested = function() {
var mainObject = this;
return {
publicNestedMethod = function() {
mainObject.privateMethod();
}
}
}();
Someone can help me please? i'm gonna loose my mind on this.
Phaedra.

Closures are a lexical feature, not a semantic one. If the object is outside the lexical scope of another, it can no longer be "nested" and access the former's local variables. In the code of your nested function/class, there's no such thing as this.privateMethod, because privateMethod is never made to be a property of MainObject. It's simply a local variable inside a function.
There's no such things as "private properties", "private methods" or "private members" in JavaScript. Hell, there's no such thing as a "class". Some people like to emulate private members using local variables as above, but doing so results in cases like this, where the discrepancy between the two concepts comes and bites one in the behind.
To conclude, it is a bad idea to write Java code, with all its OO techniques in JS, just as it is a bad idea to write C code, with all its pointers and unbounded buffers, in C#. Sure, in both cases you can do it, but you would be failing to appreciate and exploit the language's features this way.
And now that I'm done with the rant, you can do something like this to get "namespaced" functions:
MainObject = function() {
var privateVariable = "I'm private";
var privateMethod = function() {
alert('Private');
}
this.publicMethod = function() {
alert('Public');
}
this.nested = {
publicNestedMethod: function() {
privateMethod();
}
};
// or
this.nested = (function() {
var nestedPrivate = 5;
return {
publicNestedMethod: function() {
alert(nestedPrivate);
privateMethod();
}
};
})();
}
MyObject = new MainObject();
MyObject.publicMethod();
MyObject.nested.publicNestedMethod();​

Using the convention of underscore for "private" methods is a reasonable way to keep things organized.
MainObject = function() {
this._privateVariable = "i'm private";
this._privateMethod = function() {
// doSomething
}
this.publicMethod = function() {
// doPublicSomething
}
}

Well to provide the benefit of prototypal inheritance where all "subclasses" share a single instance of the method in prototype, but to ALSO provide the feature of inheriting private instances...
I came up with:
function Person(name,latentPower){
var privatesForChildren = { password:"xyz"
,latentPower:"invisibility"}
this.inherit = function(){
for(v in privatesForChildren){
eval("var " + v + "=privatesForChildren['" + v + "'];");
}
}
this.name = name;
this.revealName = function(){ alert("My name is" + this.name + "."); }
this.revealPowers = function(){ alert("I'm normal."); }
}
function Mutant(name,latentPower,fuel){
this.inherit.call(this); // Inherit private instance variables
var fuel = fuel;
this.name = name;
this.revealPowers = function(){
alert("I manifest the powers of " + latentPower + " when I " + fuel + ".");
}
}
Mutant.prototype = new Person;
Mutant.prototype.constructor = Mutant;
bob = new Person("Bob","telekenesis");
jim = new Mutant("Jim","nausea","eat pizza");
buford = new Mutant("Buford","Teflon Man","breathe");
jim.revealName(); //Inherited properly from prototype
bob.revealPowers();
jim.revealPowers();
buford.revealPowers(); //distinct from Jim's so is an "instance var"
alert(bob.latentPower); //returns undefined
alert(buford.latentPower); //returns undefined, so is "private".
How useful is that?

JavaScript Classes and Inheritance (ES6)
According to ES6, you can use JavaScript classes and inheritance to accomplish what you need.
JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript's existing prototype-based inheritance.
Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes
I'm showing the examples below with variables, but it can be applied also to functions.
Inheritance (1st Approach)
This solution can only be used with getters for your private variables, otherwise your subclass will not get access to them.
class Main {
constructor() {
let privateVariable = "private";
this.publicVariable = "public";
this.getPrivateVariable = () => {
return privateVariable;
}
}
}
Main.Sub = class Sub extends Main {
getAllVariables() {
return this.publicVariable + "-" + this.getPrivateVariable();
}
}
// Testing...
let main = new Main();
let sub = new Main.Sub();
console.log(main.privateVariable); // undefined
console.log(main.publicVariable); // "public"
console.log(sub.privateVariable); // undefined
console.log(sub.publicVariable); // "public"
console.log(main.getPrivateVariable()); // "private"
console.log(sub.getPrivateVariable()); // "private"
console.log(sub.getAllVariables()) // "public-private"
Nesting (2nd Approach)
Maybe this solution is better for you because it doesn't expose your private variables outside the Main and Nested classes.
class Main {
constructor() {
let privateVariable = "private";
this.publicVariable = "public";
Main.Nested = class Nested extends Main {
getAllVariables() {
return this.publicVariable + "-" + privateVariable;
}
}
}
}
// Testing...
let main = new Main();
let nested = new Main.Nested();
console.log(main.privateVariable); // undefined
console.log(main.publicVariable); // "public"
console.log(nested.privateVariable); // undefined
console.log(nested.publicVariable); // "public"
console.log(main.getPrivateVariable); // undefined
console.log(nested.getPrivateVariable); // undefined
console.log(nested.getAllVariables()) // "public-private"

What OO system lets you inherit private methods? Part of being private is being unaccessible from other objects.
In JS in particular, "private members" are really just local variables of the function where they are declared. JS doesn't have typical OO notions of "class", "inheritance", "public", and "private", so you can't expect to copy your OOP techniques verbatim from other OOP languages.

It is a convention. You can imitate OO Java techniques like private members but that's not recommended. You can imitate in this way:
MyFunction = function(options){
var private = {};
//to reference MyFunction as a context
var that = this;
function privateFunctionThatCallPublicMethod(){
that.publicFunction("hello");
}
this.publicFunction = function(params){
alert(params + " " + private);
}
...
}
var instance = new MyFunction({oneOption:'fsdfsad'});
This is the bests approach i found to emulate OO Java Techniques...
But there is a problem, is very inefficient...
You must use prototype instead, because otherwise it would create one object per function per instance of the "class".
MyFunction = function(options){
this._private = {};
}
MyFunction.prototype._privateFunctionThatCallPublicMethod = function(){
this.publicFunction("hello");
}
MyFunction.prototype.publicFunction = function(params){
alert(params + " " + this._private);
}
Like you think private members are (in this way) a convention.
Also, there is another thing you must know...
When you pass a function of an object as a parameter to another function you must bind the context of the function...
function bind(fnThis, fn) {
return function(){
return fn.apply(fnThis, arguments);
};
}
function makeSomething(callback){
callback("hello");
}
var instance = new MyFunction();
makeSomething(bind(instance, instance.publicFunction));
This is because you must bind "this" as instance in the body of the publicFunction, otherwise is gonna be "window" instead.

OO Javascript: good way to combine prototypal inheritance with private vars?

In OO Javascript constructor pattern: neo-classical vs prototypal, I learned that constructors using prototypal inheritance can be 10x faster (or more) than constructors using the so-called neo-classical pattern with closures as proposed by Crockford in his "Good Parts" book and presentations.
For that reason it seems like preferring prototypal inheritance seems like the right thing, in general.
Question Is there a way to combine prototypal inheritance with the module pattern to allow private variables when necessary?
What I am thinking is:
// makeClass method - By John Resig (MIT Licensed)
function makeClass(){
return function(args){
if ( this instanceof arguments.callee ) {
if ( typeof this.init == "function" )
this.init.apply( this, args.callee ? args : arguments );
} else
return new arguments.callee( arguments );
};
}
// =======================================================
var User = makeClass();
// convention; define an init method and attach to the prototype
User.prototype.init = function(first, last){
this.name = first + " " + last;
};
User.prototype.doWork = function (a,b,c) {/* ... */ };
User.prototype.method2= (function (a,b,c) {
// this code is run once per class
return function(a,b,c) {
// this code gets run with each call into the method
var _v2 = 0;
function inc() {
_v2++;
}
var dummy = function(a,b,c) {
/* ... */
inc();
WScript.echo("doOtherWork(" + this.name + ") v2= " + _v2);
return _v2;
};
var x = dummy(a,b,c);
this.method2 = dummy; // replace self
return x;
};
})();
That isn't quite right. But it illustrates the point.
Is there a way to do this and is it worth it?

preferring prototypal inheritance seems like the right thing, in general
Well... it's the more natural, native-feeling thing to do in JavaScript, certainly. But so much JavaScript does is wrong that this isn't necessarily a compliment!
Certainly when performance isn't an issue, objects that get their own bound copies of each method are easier to cope with than objects that share their methods, because you can just pass on a reference to object.method without having to make a closure-delegate or function.bind.
Is there a way to combine prototypal inheritance with the module pattern to allow private variables when necessary?
What do you want from private variables? If it's some Java-style idea of security by encapsulation, I'd give that up and just do it the Python way: put an underline on the start of the member name and anyone who wants to use from the outside will be suitably warned that it's unsupported and may screw up. There is never a security boundary inside JavaScript code executing on the same page that would warrant keeping your privates really private.
If what you want is to avoid having to locate the right copy of this when the method is called, you could manually bind methods methods in the initialiser:
var Thing= makeClass();
Thing.prototype.init= function(a) {
this._a= a;
this.showA= this.showA.bind(this);
};
Thing.prototype.showA= function() {
alert(this._a);
};
thing= new Thing(3);
setTimeout(thing.showA, 1000); // will work as `thing` has its own bound copy of `showA`
(function.bind is future-JavaScript that you can hack into the Function.prototype now until browsers support it.)
This naturally loses some of the lightweight nature of prototype-based objects, but at least you can still have them share members that aren't methods, and methods that are never going to be used as delegates, as long as it's clear and you can always remember which methods are the ones that you can use this way.
If you simply want to be able to type a private variable name without having to put this. all the time then, yeah, you'd have to do it with a closure. Your example world maybe be a little clearer called from the initialiser rather than using the first-time-self-writing:
var User= makeClass();
User.prototype.init= function(first, last){
this.name= first+' '+last;
this.method2= this._method2factory();
};
User.prototype._method2factory= function() {
var _v2= 0;
function inc() {
_v2++;
}
return function method2(a,b,c) {
/* ... */
inc();
WScript.echo('doOtherWork('+this.name+') v2= '+_v2);
return _v2;
};
};
But I'm not really sure this gets you much in comparison to just writing this._v2 and this._inc().

I'm not totally sure I understand your question. But going from what I think I do understand...
function Foo () { /*constructor*/
var counter = 0; /* private variable */
this.incrementCounter=function () { /*privileged function */
counter++
}
this.getCounter=function () { /*privileged function */
return counter;
}
}
/*public functions. Note: this pattern destroys constructor property.
Lesson: Don't depend on the constructor property! */
Foo.prototype = {
toString: function () {
var string = "";
var count = this.getCounter();
while(count--) {
string+="*"
}
return string;
}
}
var bar = new Foo();
bar.incrementCounter();
bar.incrementCounter();
bar.toString(); /* in theory, this returns "**".. haven't tested code */

You may take a look at
https://github.com/riga/jclass
I think that's what you're looking for.

Personally, I prefer the following syntax :
var keyValueStore = (function() {
// Singleton private properties
var count = 0;
var kvs = function() {
// Instance private / privileged properties
count++;
};
kvs.prototype = {
// Instance public properties
'data' : {},
'get' : function(key) { return this.data[key]; },
'set' : function(key, value) { this.data[key] = value; },
'delete' : function(key) { delete this.data[key]; },
'getLength' : function() {
var l = 0;
for (p in this.data) l++;
return l;
}
};
return {
// Singleton public properties
'create' : function() { return new kvs(); },
'count' : function() { return count; }
};
})();
With this syntax, you have a singleton object, the possibility to create instances with prototype inheritance and the possibility to define private properties at several levels.
You use it like this :
kvs = keyValueStore.create();
kvs.set('Tom', "Baker");
kvs.set('Daisy', "Hostess");
var profession_of_daisy = kvs.get('Daisy');
kvs.delete('Daisy');
console.log(keyValueStore.count());