I am involved in a web application project at the moment and we are not going to be using a framework.
I am looking for the 'best' javascript inheritance implementation. I have worked with prototypal style classes as follows:
function animal(options) {
self = this;
//properties
this.name = options.name;
//events
this.onXYZ = options.onXYZ;
//event handlers
this.handlerOfEvent = function() {
//do something using 'self' as the 'this' variable
}
}
animal.prototype.aFunction = function()
{
//do something
}
etc.
I have not used inheritance without a framework (usually use Mootools) but I do understand to a point how it works in Javascript and have seen a fair few implementations.
I wanted to get some feedback on where I could find the best implementation, one that doesn't fiddle with any native types and allows me full access to the ascendant classes' properties and functions.
Any pointers would be greatly appreciated.
Thanks very much for your time.
There's a method described by (who else) Douglas Crockford that I've been partial to as of late:
var rectangle = function(width, height)
{
var h = height, w = width;
var scale = function(s)
{
h = h * s;
w = w * s;
}
return { scale: scale };
}
var square = function(width)
{
var o = rectangle(width, width)
// Add things to o, if needed
return o;
}
Not a terribly good example, as nothing is really being extended, but it should get the idea across. In order to instantiate these objects, simply use this:
var newRectangle = rectangle(3, 4); // 3 by 4 rectangle
var newSquare = square(6); // 6 by 6 square
I tried many approaches in the past. I like John Resig way of implementation the most. It's very simple. You can see full example and javascript file (only around 25 lines of code) from http://ejohn.org/blog/simple-javascript-inheritance/
Just to complete the answer, you can implement a class like this after include his code..
var Person = Class.extend({
name : '',
init : function (name) {
this.name = name;
},
say : function () {
alert("I'm " + this.name);
}
});
var mick = new Person("Mick");
mick.say();
Take a look at Simple Javascript Class Project (constant, property, protected, static, utils, and more), Simple JavaScript Inheritance and Inheritance Patterns in JavaScript.
Simple Javascript Class (sjsClass) Example
Class.extend('Foo', {
__protected : {
privV : 123,
privF : function () {
return this.privV + this.priv3;
}
},
'protected priv3' : 'Protected Value',
setX : function (x) {
this.privV = x;
},
test : function () { return this.privF(); }
});
var f = new Foo;
f.setX(456);
f.test(); // -> 'Protected Value456'
f.privF(); // -> Error
f.privV; // -> undefined
f.priv3; // -> undefined
You should check the videos from Douglas Crockford about "parasatic inheritance".
Here's a basic example
var pkg={};//simulating a package
pkg.ObjA=function (){
var privateField;//every inner function will have a closure to this field, this is the way to simulate private fields
var privatefunc=function(){
//same for private functions
};
//use object augmentation to add different fields to the "that" reference
that.publicMethod=function(){
//do something
};
return that;
}
//create two different instance of the object A
var instance1=pkg.ObjA();
var instance2=pkg.ObjA();
pkg.ObjB=function(){
//the that of this object is based on the ObjA
var that=pkg.ObjA();
//specialize the that to simulate inheritance
that.newMethod=function(){
}
return that;
}
var child=pkg.ObjB();
Related
For a client side JS application, I require creating Quizzes and Surveys. The domain logic for these objects is incredibly similar so I would like them to both inherit from one UserInput object, while they each have very few additional methods each.
I'm concerned with the best practice method of doing this. I was thinking right off the top of my head I can just create a UserInput constructor that acts as a prototype, and then dynamically add methods to both Quizzes and Surveys.
For instance:
function UserInput() {}
UserObject.prototype.sharedMethod = function() {}
Quiz = new UserInput();
Quiz.sharedMethod()
Quiz.quizMethod = function() {}
Survey = new UserInput();
Survey.surveyMethod = function() {}
Survey.sharedMethod()
However I wonder if this is just not plain monkey-patching, and implementing a similar idea to abstract classes in JavaScript would be cleaner.
var Quiz = function() {
UserInput.apply(this, arguments)
}
Quiz.prototype = UserInput();
Quiz.prototype.constructor = quiz;
Quiz.prototype.quizMethod = function() {}
The immediate difference I see is in the first example quiz/survey are objects while in the second quiz is a prototype. Every page has a singleton of these items, so having a method on every instance of quiz (which is only one) does not seem that bad to me.
Which is preferred and why? (Or am I missing any better methods of instantiating objects).
The one I use is available on github and it works well for me with a simple familiar sytax. Allows OOP concepts in javascript including classes, inheritance, multi-inheritance, polymophism, interfaces (code contracts), and enumerators
Heres an example of simple class inheritance:
/* using ds.oop.min.js */
var a= ds.class({
type: 'a',
constructor: function (x) { this.x = x; },
mul: function (s) {
this.x *= s;
return this;
}
});
var b= ds.class({
type: 'b',
inherits: a,
constructor: function (x) { this.x = x; },
sub: function (s) {
this.x -= s;
return this;
}
});
var o = new b(5);
var output = o.mul(3).sub(5); // output = 10
I found different ways that seem to work.
Mostly recommended way in textbooks and the internet:
var Person = function() {
this.age = 23;
}
Tony = new Person();
This also seems to work:
function Person() {
this.age = 23;
}
Tony = new Person();
Is there a difference? And an additional question: Usually you cannot simply leave out parentheses. Here it is possible (new Person instead of new Person()). This is because of using the new keyword, right?
A third odd way that I just tried out looks like this:
function Person() {
return {age: 2};
}
Tony = new Person();
Tony = Person(); // both ways work! It seems that you can leave out 'new' here.
Here I don't get an object with the name of my class, but my property is also accessible and it seems like it was quite similar to both above approaches.
What shall I use and what are the technical differences? Thank you!
JavaScript is a classless language. Classes don't exist, but objects may inherit properties from each other by using prototypes. This means you are not limited to implementing inheritance in a class-like manner. Personally, I like to use a BackboneJS-inspired method (code requires UnderscoreJS):
var BaseObject = function(){}; //Create a function so that we may use the new operator.
//There may be code in the constructor
BaseObject.extend = function(obj) { //Add a static function to the BaseObject to extend it
var base = this; //Save a reference for later
//Create the constructor for the sub object. We need to extend it, so we can't use the base constructor. AFAIK, this is the only way to clone the base constructor, i.e. by creating a new function that calls it
var SubObject = _.extend(function(){
base.apply(this, arguments); //Call base constructor
}, this);
SubObject.prototype= _.extend({}, this.prototype, obj); //Create new prototype that extends the super prototype, but does not overwrite it.
return SubObject; //Return the new constructor + prototype
};
This allows you to do cool class-like stuff like this:
var Car = BaseObject.extend({
speed: 0,
acceleration: 5,
accelerate: function(){
this.speed += this.acceleration;
}
});
var RaceCar = Car.extend({
acceleration: 10,
});
var car = new Car();
var raceCar = new RaceCar();
car.accelerate();
raceCar.accelerate();
if(raceCar.speed > car.speed){
console.log('raceCar won');
}else{
console.log('car won');
}
For more information on inheritance in JavaScript, I strongly recommend reading JavaScript: The Good Parts by Douglas Crockford.
Regarding your examples:
The difference between 1 and 2 is minimal. For more information see this question.
In 3, you are just returning an object literal. The new keyword only has influence on the this keyword within the function, which you are not using, and so using new has no effect. For more information, see this quesion
1 and 2 (var x = function vs function x) are very similar. 3 is a completely different thing.
The difference between 1 and 2 has nothing to do with classes and has been asked before on SO (several times). I think the most complete answer is this one:
https://stackoverflow.com/a/338053/1669279
In short, the first x points to an anonymous function and some debugging tools might have problems with that. The first one is available from the line it was defined on while the second is available in the entire scope. Read the linked answer for details.
The 3rd "solution" is not a class at all. It is simply a function that returns an object (might be called a Factory method).
It is not a good idea to return things from your constructors, especially return this. You should only return things if you want to override the normal process of creating objects (like implementing the singleton pattern for example).
As a side-note, you should always use new when you instantiate a class. Here is what happens when you try to be smart and save characters:
function X () {
return this;
}
console.log(X()); // outputs the window object
The parenthesis after calling the constructor with no parameters are optional, but it is frowned upon to avoid them because it results in slightly more confusing code.
To sum it up, i usually use pattern 1. Pattern 2 is also ok.
One problem with pattern 2 can be this one:
var x = new X(); // works
console.log(x.message); // works, I am X
x.method(); // doesn't work, method hasn't been defined yet
function X() {
this.message = 'I am X';
}
X.prototype.method = function() {
console.log(this.message);
};
this is how i do mine:
;(function (window) {
"use strict";
//-- Private Vars
var opt, obj, rm, Debug;
//-- construtor
function App(requestedMethod) {
//-- set up some vars
if(typeof requestedMethod !== 'undefined') {
rm = requestedMethod;
}
opt = {
rMethod: (typeof rm !== 'undefined') ? (rm != null) ? rm : false : false
}
//-- containe resulable objects
obj = {}
//-- call the init method
this.init();
}
/** Public Methods **/
/**
* The Init method called on every page load
*/
App.prototype.init = function () {
var om = opt.rMethod;
//-- Once all init settings are performed call the requested method if required
if(om) {(typeof App.prototype[om] == 'function') ? App.prototype[om]() : _DB('Call to Method [' + om + '] does not exsist.');}
};
/**
* testmethod
*/
App.prototype.testmethod = function () {
};
/** Private Methods **/
function PrivateMethod(){
}
/**
* A console output that should enable to remain enable js to work in IE
* just incase i forget to remove it when checking on those pesky IE browsers....
*/
function _DB(msg){
if(window.console && window.console.log){
var logDate = new Date();
window.console.log('------------------- ' + logDate + ' ----------------------------------');
window.console.log(msg);
}
};
window.App = App;
})(window);
then call it like:
<script src="ptha/to/your/app.js"></script>
<script>$(function() { new App('testmethod'); });</script>
When the code is loaded the new App() will then run once all page load data has completed
Hope this helps.To get access to it outside add the new to a var
var App = new App('testmethod);
then you can access things like
App.testmethod()...
var Person = function() {
this.age = 23;
}
Person is a variable that contains(is referenced) an anonymous function
function Person() {
this.age = 23;
}
but here you declare a function called "Person"
function Person() {
return {age: 2};
}
and so you declare a function that returns a new static object.
The best way depends on the needs, if you want to declare classes use the second, while to create the modules uses the third. For the first method look here: http://helephant.com/2008/08/23/javascript-anonymous-functions/
I've put these together with the help of others and several resources. I've made a fiddle of everything, and the stripped down code is posted below.
Basically I've learned how to use each of these patterns but I'm curious about the more fundamental differences between these approaches. Downstream code is practically identical with any of these patterns, but is there a reason why one should use one over another, beyond personal preference? Also though I've tried to gather up the most common patterns, please suggest your own if it's better.
Pattern 1 (Object Based):
var mouseDiff = {
"startPoint" : {"x" :0, "y" : 0},
"hypotenuse" : function(a,b) {
// do something
},
"init" : function(){
// do something
}
}
mouseDiff.init();
Pattern 2 (Most traditional as far as I know):
function MouseDiff() {
this.startPoint = {"x" :0, "y" : 0};
}
MouseDiff.prototype.hypotenuse = function(a,b) {
// do something
}
MouseDiff.prototype.init = function() {
// do something
}
var myMouse = new MouseDiff;
myMouse.init();
Pattern 3 (Making use of closure):
var MouseDiff2 = (function() {
var startPoint = {"x" :0, "y" : 0};
var hypotenuse = function(a,b) {
// do something
};
return {
hypotenuse: hypotenuse,
init : function(){
// do something
}
};
}());
MouseDiff2.init();
Pattern 1 is a singleton. If you only need one such object, it's just fine.
Pattern 2 builds new objects, and takes advantage of the prototype object so that when a new MouseDiff object is created, it will not create new copies of the functions (which are themselves data in JavaScript).
Pattern 3 requires more memory in comparison to a regular singleton but it offers static privacy.
I like the following pattern, as it covers various features, though it is really a combination of the constructor (pattern 2) and closure (pattern 3):
var MouseDiff = (function () {
var aStaticVariable = 'Woohoo!';
// And if you really need 100% truly private instance
// variables which are not methods and which can be
// shared between methods (and don't mind the rather
// big hassle they require), see
// http://brettz9.blogspot.com/search?q=relator
// (see also the new plans for a Map/WeakMap in ECMAScript)
function _APrivateStaticMethod () {
alert(aStaticVariable);
}
// An instance method meant to be called on the
// particular object as via ".call(this)" below
function _APrivateInstanceMethod () {
alert(this.startPoint.x);
}
// Begin Constructor
function MouseDiff() {
this.startPoint = {"x" :0, "y" : 0};
}
MouseDiff.prototype.hypotenuse = function(a,b) {
// do something
};
MouseDiff.prototype.init = function() {
// do something
_APrivateStaticMethod(); // alerts 'Woohoo!'
_APrivateInstanceMethod.call(this); // alerts 0 (but if not
// called with this, _APrivateInstanceMethod's internal
// "this" will refer (potentially dangerously) to the
// global object, as in the window in the browser unless
// this class was defined within 'strict' mode in which
// case "this" would be undefined)
};
return MouseDiff;
}());
var myMouse = new MouseDiff;
myMouse.init();
I do not know enough about JavaScript to tell you what if any performance differences exist between these approaches. Here are just two differences between these I noticed. I'm sure there are others.
Pattern 1 creates one object with those properties, including attached methods. Pattern 2 allows us to easily create many objects with the same methods attached, without rewriting them.
Pattern 3 is like a factory. Instead of relying on prototype to automatically attach these methods, the factory just creates them anew and returns the object. The usage of a closure allows us to hide the "member variables" of the object. There is no way to access startPoint or hypotenuse() except through the "public" interface returned.
Whenever I answer these types of theoretical JavaScript questions, I always fear there is some technical detail I am forgetting or overlooking. If so, let me know, and I will fix the answer.
Pattern two is my personally preference because it is the closest to traditional object oriented programming and allows for easy inheritance.
This post by John Resig (the guy behind JQuery) uses that method...
http://ejohn.org/blog/simple-javascript-inheritance/
[edit]
In fact, I don't think methods 1 or 3 have any benefits. 1 is, as someone else said, a singleton and does not allow multiple instances and 3... I don't know where to start with 3.
There is one more possible way to do this.
var MouseDiff = {};
(function(context) {
var privateVarialble = 0;
context.hypotenuse = function() {
//code here
};
context.int = function() {
//code here
}
})(MouseDiff);
Here we simply pass the namespace as an argument to a self-invoking function. The privateVarialble variable is private because it does not get assigned to the context.
We can even set the context to the global object (with a one word change!). Inside brackets (MouseDiff) make it (this). This is a big asset for library vendors – who can wrap their features in a self-invoking function and leave it to the user to decide whether they should be global or not.
http://www.jsoops.net/ is quite good for oop in Js. If provide private, protected, public variable and function, and also Inheritance feature. Example Code:
var ClassA = JsOops(function (pri, pro, pub)
{// pri = private, pro = protected, pub = public
pri.className = "I am A ";
this.init = function (var1)// constructor
{
pri.className += var1;
}
pub.getData = function ()
{
return "ClassA(Top=" + pro.getClassName() + ", This=" + pri.getClassName()
+ ", ID=" + pro.getClassId() + ")";
}
pri.getClassName = function () { return pri.className; }
pro.getClassName = function () { return pri.className; }
pro.getClassId = function () { return 1; }
});
var newA = new ClassA("Class");
//***Access public function
console.log(typeof (newA.getData));
// function
console.log(newA.getData());
// ClassA(Top=I am A Class, This=I am A Class, ID=1)
//***You can not access constructor, private and protected function
console.log(typeof (newA.init)); // undefined
console.log(typeof (newA.className)); // undefined
console.log(typeof (newA.pro)); // undefined
console.log(typeof (newA.getClassName)); // undefined
This has been answered elsewhere many times before but just to offer up some variety. ds.oop is a nice way to declare classes with constructors in javascript. It supports every possible type of inheritance (Including 1 type that even c# does not support) as well as Interfaces which is nice.
var Color = ds.make.class({
type: 'Color',
constructor: function (r,g,b) {
this.r = r; /* now r,g, and b are available to */
this.g = g; /* other methods in the Color class */
this.b = b;
}
});
var red = new Color(255,0,0); // using the new keyword to instantiate the class
I'm having a little trouble working out how my JavaScript should be structured, etc..
My OOP skills in languages such as PHP, ActionScript 3 and so on are what I'm assuming to be on-par, but JS is lacking this which has thrown me off quite a bit in my learning.
I have a vague understanding of the prototype feature which I used a little in AS2 - I believe this is the closest I'll be able to get. At the moment, I'm laying out my code similar to this:
var slideshow =
{
property: value,
/**
* This is a method
*/
myMethod: function()
{
// do method things
}
};
// ------
slideshow.property ++;
slideshow.myMethod();
This all works okay, but it's void my ability to do something like:
var myslideshow1 = new Slideshow();
var myslideshow2 = new Slideshow();
myslideshow1.property = 10;
myslideshow2.property = 16;
I'm not sure on how to go about creating two different instances of one "object" I've created (in this case, slideshow).
I can't find any resources that explain the prototype feature in a way that makes sense.
Any pointers would be supoib.
Any javascript function can act as a constructor for a class, so try this:
function SlideShow(params) {
return {
property: value,
myMethod: function() {
//do method things
};
};
};
var slideshow1 = new SlideShow(params);
slideshow1.property = 10;
//etc.
I would frown apon using prototype to add methods to a class as there could be performance issues
Here is a sample class structure you could use. JavaScript classes are not much different the functions.
function MyItem(){
this.d = '';
this.clear = function( ) {
this.d = '';
}
}
var myItem = new MyItem( )
myItem.d = "test";
alert(myItem.d);
myItem.clear();
alert(myItem.d)
Some good reading here
You should avoid using the new operator, everything is public. A better way to do what you want to do, and have private variables and functions is to do the following:
var slideshow = function () {
var self = {};
var private_param = "hello";
var private_func = function(say) {
alert(say);
};
var method = function() {
private_func(private_param);
};
var param = 500;
self.method = method;
self.param = param;
return self;
// return object, with the method func and param param publicly accessible
// private_param and private_func are not accessible to the outside
};
var presentation = slideshow(); // new slideshow, you could edit to pass in init params
presentation.method(); // hello
I need some simple objects that could become more complex later, with many different properties, so i thought to decorator pattern.
I made this looking at Crockford's power constructor and object augmentation:
//add property to object
Object.prototype.addProperty = function(name, func){
for(propertyName in this){
if(propertyName == name){
throw new Error(propertyName + " is already defined");
}
}
this[name] = func;
};
//constructor of base object
var BasicConstructor = function(param){
var _privateVar = param;
return{
getPrivateVar: function(){
return _privateVar;
}
};
};
//a simple decorator, adds one private attribute and one privileged method
var simpleDecorator = function(obj, param){
var _privateVar = param;
var privilegedMethod1 = function(){
return "privateVar of decorator is: " + _privateVar;
};
obj.addProperty("privilegedMethod1", privilegedMethod1);
return obj;
}
//a more complex decorator, adds public and private properties
var complexDecorator = function(obj, param1, param2){
//private properties
var _privateVar = param1;
var _privateMethod = function(x){
for(var i=0; i<x; i++){
_privateVar += x;
}
return _privateVar;
};
//public properties
var publicVar = "I'm public";
obj.addProperty("publicVar", publicVar);
var privilegedMethod2 = function(){
return _privateMethod(param2);
};
obj.addProperty("privilegedMethod2", privilegedMethod2);
var publicMethod = function(){
var temp = this.privilegedMethod2();
return "do something: " + temp + " - publicVar is: " + this.publicVar;
};
obj.addProperty("publicMethod", publicMethod);
return obj;
}
//new basic object
var myObj = new BasicConstructor("obj1");
//the basic object will be decorated
var myObj = simpleDecorator(obj, "aParam");
//the basic object will be decorated with other properties
var myObj = complexDecorator(obj, 2, 3);
Is this a good way to have Decorator Pattern in javascript?
Are there other better ways to do this?
There are various implementations of the Decorator pattern in Javascript on Wikipedia and other sites - (1), (2), (3). The pattern is defined as:
the decorator pattern is a design pattern that allows new/additional behaviour to be added to an existing object dynamically.
Object extension is already build into the language itself. Objects can be easily extended, and properties can be added anytime. So why should you have to jump through hoops to achieve this? Shouldn't something like this suffice:
var person = { name: "Jack Bauer" };
// Decorated the object with ability to say a given phrase
person.say = function(phrase) {
alert(phrase);
}
// Using the decorated functionality
person.say("Damn it!");
If you want a method to apply to all objects that were created using this function, then add that method/properties to the function's prototype.
Update: If you have clearly defined pieces of functionality which can be mixed and matched as needed into certain types of objects, then the MooTools approach of extending and mixing in behavior into objects is nicely done. To give an example, consider a UI component that can be resized, dragged around with a handle, and deleted by clicking a tick mark at the top-right corner. You may not want to create each component with these behaviors but define all these behaviors separately each into their own object. And later mix in these behaviors into each type of component as needed.
var Resizable = {
...
};
var Draggable = {
...
};
var Deletable = {
...
};
var someLabel = new Label("Hello World");
// one way to do it
someLabel.implement([Resizable, Draggable, Deletable]);
// another way to do it
someLabel.implement(Resizable);
someLabel.implement(Draggable);
someLabel.implement(Deletable);
It looks better and more intuitive (to me) than doing something like
var awesomeLabel = new Resizable(new Draggable(new Deletable(someLabel)));
because we are still dealing with a label, and not some resizable, or some draggable, or some deletable object. Another small point, but still worth mentioning is that the parentheses start getting unmanageable after 3 or 4 decorators, especially without good IDE support.