Best way to call a function in javascript [closed] - javascript

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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;
}
}

Related

javascript class in hta [duplicate]

how to create a class in classic jscript? (not jscript.net)
And, how to reference this class?.
I tried with
class someclass {
}
but it does not work.
There are no classes in jscript. You can make an object constructor:
function someclass() {
this.answer = 42;
}
You use it like a class:
var obj = new someclass();
To make methods you add functions to its prototype:
someclass.prototype.getAnswer = function() {
return this.answer;
}
Usage:
var ans = obj.getAnswer();
There are not classes as such, but here's a simple example of how to get basic object-oriented functionality. If this is all you need, great, but if you're after other features of classes, such as inheritance, someone more knowledgeable than myself will have to help.
function SomeClass(n) {
this.some_property = n;
this.some_method = function() {
WScript.Echo(this.some_property);
};
}
var foo = new SomeClass(3);
var bar = new SomeClass(4);
foo.some_method();
bar.some_property += 2;
bar.some_method();
Most recent:
JavaScript/Reference/Classes
Answer from 2011:
You don't really have classes on Javascript, but you have something similar. Check this example on jsFiddle
var classA = function() { // declaring a "class"
this.something = "Text"; // a public class field
};
classA.prototype.b = " b "; // a class field
classA.c = "c"; // a static field
classA.prototype.d = function(x) { // a public class method
};
classA.e = function(x){ // a public static method
};
var a = new classA(); // instantiate a class
Read more on MDC...
Define a function with the name of the class. Any var defined within it as this.whatever will act as a class member:
function SomeClass() {
this.a;
this.b;
}
Then add methods to the prototype:
SomeClass.prototype.methodA = function() {
this.a++;
}
SomeClass.prototype.methodB = function() {
this.b++;
}
I believe you can also define methods inside the constructor like this, but I've not used this syntax for a long time.
function SomeClass {
this.a = 0;
// Method definition
this.methodA = function() {
this.a++;
}
}
Bear with me as I only faintly grasp this myself:
Javascript does not have classes. It has objects. To replicate a class, you create an object. To create "instances" of that "class", you duplicate that object. There are a few ways to do this. One is to create a function that returns an object, then call the function, like so:
function Car(brand, year) {
return {
brand: brand,
year: year
}
}
var modelT = Car("Ford", 1900); //or whenever the model T came out
modelT.brand == "Ford" //true
modelT.year == 1900; //true
Another way is to create an object that is a function and create a "new" of that object. The catch is you have to use new, and that's rather misleading.
var Car = function(make, year) {
this.make = make;
this.year = year;
};
var x = new Car("ford", 1990);
//same tests hold true from earlier example
In my opinion the best way is to use Object.create because it best represents what's actually happening:
var Car = (function() {
var self = Object.create({}, {
make: {
value: "Ford"
}
year: {
value: 1900
}
});
return self;
})();
var modelT = Object.create(Car, {
make: {
value: "Model T"
},
year: {
value: 1901
}
});
Unfortunately, this is extremely cumbersome.
Edit:
This is an extremely helpful resource: JavaScript "classes"
Classes in Jscript (.Net?): http://www.functionx.com/jscript/Lesson05.htm
And Powershell supports it (as well as VisualBasic, even F#). Now I see the question says not in .net. But in my defense, I was googling jscript classes, and this is where I landed.
Add-Type #'
class FRectangle {
var Length : double;
var Height : double;
function Perimeter() : double {
return (Length + Height) * 2; }
function Area() : double {
return Length * Height; } }
'# -Language JScript
[frectangle]::new()
Length Height
------ ------
0 0

Class vs alternate ways of accomplishing it [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();

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();

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.

Object oriented JavaScript with example [closed]

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I am aware of general Object-oriented programming principles like Encapsulation, Inheritance, Polymorphism, Abstraction, etc
But would now want to understand these concepts from a JavaScript perspective.
Could someone take a very basic example and run how these works in JS context (Encapsulation, Inheritance, Polymorphism, Abstraction)
I have read a lot about these online, but the articles have left me more confused.
Thank you.
I will describe the Douglas Crockford Pattern to mimic the style used in Object-Oriented Programming languages. It doesn't use prototypal inheritance. As a result, it's slightly less efficient because each object has to store a reference to each method. But it's very useful for illustrative purposes.
Encapsulation:
function MyClass (a, b)
{
this.publicProperty = 1;
var _privateProperty = 2;
function _privateMethod () {
// only private methods and privileged methods can call this
};
this.publicMethod = function () {
// can access _privateProperty and call _privateMethod
};
}
MyClass.classMethod = function () {
// not tied to any instances
};
Simply create objects with var instance = new MyClass(a, b);
Inheritance:
function DerivedClass(a, b, c)
{
// must explicitly call superclass constructor, like in Java
MyClass.apply(this, arguments);
this.anotherProperty = 3;
function _anotherPrivateMethod() { };
this.publicMethod = function () {
// can access _privateProperty and call _privateMethod
};
}
DerivedClass.classMethodMethod = function ()
{
// not tied to any instances
};
Polymorphism in JavaScript is mostly replaced by Duck Typing (http://en.wikipedia.org/wiki/Duck_typing). Developers usually group methods/properties under objects, and you just test for the presence of those objects. This is how newfangles browser capabilities are detected, for instance.
Abstraction is closely tied with the polymorphism - as long as something supports an interface, you don't usually care how it works underneath. Thus, you may download a Javascript library and just use it, based on its documentation.
Hope this helps.
I think the most interesting is encapsulation as a lot of people don't use it properly.
Lets take a simple object as an example
var Person = function( firstName, lastName, isMr ) {
var prefix = isMr ? "Mr." : "Mrs." ;
this.getFullName = function() { return prefix + " "
+ firstName + " " + lastName }
}
var p = new Person ("guy","mograbi", true);
p.getFullName(); // => "Mr. guy mograbi"
// p.prefix ==> causes an error.
Inheritance - is simply extending the prototype
var Superhero = function(){
Person.call(this);
}
However proper inheritance is an issue by itself.
Check out https://stackoverflow.com/a/4985616/1068746
Polymorphism - is quite simple, given a new prototype that implements "getFullName"
var Child = function(){
this.getFullName = function(){ return "not allowed to talk with strangers" }
}
given function(a){ a.getFullName() }
You will get full name if a is Person and "not allowed.." if a is Child.
Abstraction - is more of a type-safe language thing.
https://stackoverflow.com/a/4082496/1068746
You can use a function to define a singleton object
var apple = new function() {
this.type = "macintosh";
this.color = "red";
this.getInfo = function () {
return this.color + ' ' + this.type + ' apple';
};
}
use it as given below
apple.color = "reddish";
alert(apple.getInfo());
new function(){...} does two things at the same time: define a function (an anonymous constructor function) and invoke it with new.

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