I try to understand OOP in JavaScript.
I want to create object Person and Worker. Worker inherits Person. I wrote code:
function Person(name, age) {
this.name = name;
this.age = age;
}
Person.prototype.grow = function () {
this.age++;
console.log('Person grows, new age ' + this.age);
};
function Worker(name, age, position) {
// How to call parrent constructor Person?
this.position = position;
}
Worker.prototype = Person.prototype;
Worker.constructor = Worker.prototype.constructor;
Worker.prototype.promote = function () {
console.log('Worker ' + this.name + ' became Senior ' + this.position);
};
Worker.prototype.grow = function () {
this.promote();
// How to call parrent method grow?
};
var workerObj = new Worker('Ben', 39, 'engineer');
workerObj.grow();
But in JS variable assignment works by reference and expression Worker.prototype = Person.prototype; doesn't get result and method grow in Worker overrides method grow in Person and I will not be able to get access to parent method.
I know that I need to use third object. But is there way to inherit without third object?
Setting the functions' .prototype properties to the same object essentially makes them the same class, as you've noticed. What you really need, is for Person.prototype to be an object that inherits from Worker.prototype. But you need to do this without calling the Person constructor, since that leave some side effects back in the prototype chain (they aren't significant in the case you mention, but they could be significant in other cases). So Worker.prototype = new Person(); isn't an ideal solution for you.
Object.create() works for this. Among other things, this function can be used to create an object that inherits from another, without calling any constructors. For the situation you're talking about, it would look like this:
Worker.prototype = Object.create(Person.prototype);
Worker.prototype.constructor = Worker;
Object.create doesn't work in older versions of IE, and a total polyfill isn't available due to engine limitations. But there are polyfills for Object.create which work well enough to enable this kind of subclassing, so browser support need not be an issue.
I typically wrap this up in a function, so that once I've defined my subclass and superclass, I can express the relation without much extra rigamarole. You could do that like this:
Object.subclass = function (sub, sup) {
sub.prototype = Object.create(sup.prototype);
sub.prototype.constructor = sub;
}
Object.subclass(Worker, Person); // "class Worker extends Person"
I make inheritance in javascript like this :
var c_Parent = function () {
};
var c_Child = function () {
c_Parent .call(this);
};
c_Child.prototype = new c_Parent();
c_Child.prototype.constructor = c_Child;
So in you case :
function Person(name, age) {
this.name = name;
this.age = age;
}
Person.prototype.grow = function () {
this.age++;
console.log('Person grows, new age ' + this.age);
};
function Worker(name, age, position) {
this.position = position;
Person.call(this, name, age);
}
Worker.prototype = new Person();
Worker.prototype.constructor = Worker;
Worker.prototype.promote = function () {
console.log('Worker ' + this.name + ' became Senior ' + this.position);
};
Worker.prototype.grow = function () {
this.promote();
Person.prototype.grow.call(this);
};
var workerObj = new Worker('Ben', 39, 'engineer');
workerObj.grow();
I'm working on a fairly complex object in JS and I'm running into issues:
I have the following (abridged) code:
var LocationSelector;
LocationSelector = function(container) {
this.selectors = {
container: container,
city_name: container.find('input.city_name'),
city_id: container.find('input.city_id')
};
return this.initialize();
};
LocationSelector.prototype = {
initialize: function() {
return this.city.checkStatus();
},
city: {
status: null,
message: null,
id: null,
checkStatus: function() {
if (LocationSelector.selectors.city_name.val() && LocationSelector.selectors.city_id.val()) {
return LocationSelector.city.setStatus('success');
}
},
setStatus: function(status) {
return alert(status);
}
}
};
Two questions:
1) Inside of a sub-object function this no longer refers back to the root object. It seems I can refer back to the parent if I write out LocationSelector.object.method( args ), but that's a lot to type. Is there a way to define a shortcut back to the parent object?
2) In some situations I need to have several instances of this per page, so it's important to me that I can set the various selectors when a new object is instantiated and then refer to the instance selectors in the prototype. Is referring to the parent object (ie. LocationSelector) in sub-object methods even viable for that? How does JS know to stay with the currently active object's stored properties?
Basically, I'm trying to implement a class, and I'm totally new to JS and don't really know how to do it. So, any help or suggestions are appreciated. Thanks!
There are many things wrong with your current approach. Here is something closer to what you want, although I do not understand why LocationSelector instances have a city member.
function LocationSelector(container) {
this.selectors = {
container: container,
city_name: container.find("input.city_name"),
city_id: container.find("input.city_id")
};
this.city = new City(this);
this.city.checkStatus();
}
function City(locationSelector) {
this.status = null;
this.message = null;
this.id = null;
this.locationSelector = locationSelector;
}
City.prototype.checkStatus = function () {
if (this.locationSelector.selectors.city_name.val() && this.locationSelector.selectors.city_id.val()) {
this.setStatus("success");
}
};
City.prototype.setStatus = function () {
alert("status");
};
Things to note:
Data properties go on the instance, not the prototype. Only methods go on the prototype.
City is clearly its own class, so you should make it one. In your code, a single city is being shared between all instances of LocationSelector, since it is put on the prototype. In this code, it is assigned as an instance property, in the LocationSelector constructor.
You cannot reference LocationSelector.selectors like you do in your example. LocationSelector.selectors would be for "static" properties, which LocationSelector does not have. Instead you need to refer to the selectors property on specific instances; in this example, that instance is given by this.locationSelector.
Points 2 and 3 speak to an important fact: the "child" City instance cannot reference to properties of the "parent" LocationSelector class without having a concrete instance of it.
Here is a version of the code that makes more sense to me, removing the part where LocationSelector has a city property (which it doesn't use).
function LocationSelectors(container) {
this.city_name = container.find("input.city_name");
this.city_id = container.find("input.city_id");
}
function City(locationSelectors) {
this.locationSelector = locationSelector;
}
City.prototype.checkStatus = function () {
if (this.locationSelectors.city_name.val() && this.locationSelectors.city_id.val()) {
this.setStatus("success");
}
};
City.prototype.setStatus = function () {
alert("status");
};
function checkCityStatus(container) {
var locationSelectors = new LocationSelectors(container);
var city = new City(locationSelectors);
city.checkStatus();
}
I leave you with a link to Crockford's "Private Members in JavaScript", which talks about doing OO in JavaScript. There are other, probably better explanations out there, but at least that one will put you on the right track.
Read about Closures and I'm positive you will find what you need.
Here's is a quick example of what you are trying to accomplish:
function MyCoolObject(name){
var self_myCoolObject = this;
this.name = name;
this.popAlertWithNameInFiveSeconds = function(){
setTimeout(function(){
alert('Incorrect reference to name "this.name" returns ' + this.name);
alert('Correct reference to name "self_myCoolObject.name" returns ' + self_myCoolObject.name);
},5000)
}
}
//TO TEST
var MyObj = new MyCoolObject('MySuperCoolName')
MyObj.popAlertWithNameInFiveSeconds();
Here is a snippet of JS code that I have. Before I drop down into a click handler, I make a reference to the object (SlideShow) by calling var parent = this. Then in later nested functions, you can be sure you're calling the right scope by using parent.function()
/* Slide Show object */
function SlideShow(parentContainerId) {
this.BEGINNING = 'Beginning';
this.END = 'End of list';
this.FIRSTINDEX = 0;
this.length = jQuery(parentContainerId + ' img').length;
this.container = jQuery(parentContainerId);
this.imgs = jQuery(parentContainerId + ' img');
this.index = this.FIRSTINDEX;
this.status = 'beginning'; // beginning, end
this.init = function() {
// get it started
this.moveTo(this.FIRSTINDEX);
this.process();
// ****GET OBJECT SCOPE*****
var parent = this;
// set up click listener
this.container.find('img').click(function(e) {
var item_width = jQuery(this).width();
var x_click_ps = e.clientX - jQuery(this).offset().left;
var x_diff = x_click_ps / item_width;
console.log(this);
if (x_diff < .5) {
parent.moveByIncrement(-1)
parent.process();
} else {
parent.moveByIncrement(1);
parent.process();
}
});
}
.
.
.
}
Just for the kicks i am trying to create a simple data object in javascript. Here is the code.
var roverObject = function(){
var newRover = {};
var name;
var xCord;
var ycord;
var direction;
newRover.setName = function(newName) {
name = newName;
};
newRover.getName = function() {
return name;
};
newRover.setDirection = function(newDirection) {
direction = newDirection;
};
newRover.getDirection = function() {
return direction;
};
newRover.setXCord = function(newXCord) {
xCord = newXCord;
};
newRover.getXCord = function() {
return xCord;
};
newRover.setYCord = function(newYCord) {
yCord = newYCord;
};
newRover.getYCord = function() {
return yCord;
};
newRover.where = function(){
return "Rover :: "+ name +" is at Location("+xCord+","+yCord+") pointing to "+direction;
};
return newRover;
};
rover1 = new roverObject();
rover2 = new roverObject();
rover1.setName("Mars Rover");
rover1.setDirection("NORTH");
rover1.setXCord(2);
rover1.setYCord(2);
console.log(rover1.where());
console.log(rover1);
rover2.setName("Moon Rover");
rover2.setDirection("SOUTH");
rover2.setXCord(1);
rover2.setYCord(1);
console.log(rover2.where());
console.log(rover2);
There are few questions that I have around this creation.
I want to create an object where the properties/attributes of object are private and not visible to world. Am I successful in doing that? Can I really not access the object attributes?
Is there a better way to create this kind of object?
If I want to inherit this object, I should do a newObject.prototype = roverObjectwill that work? And will that make sense most of all.
Finally I have a wierd problem. Notice the last method of objet "where" which returns a concatenated string. Here I tried following code instead.
newRover.where = function(){
return "Rover :: "+ name +" is at Location("+xCord+","+yCord+") pointing to "+direction;
}();
and then did a following console.log
console.log(rover1.where);
console.log(rover2.where);
It threw following error for me:
cannot access optimized closure
Why would it say that? What am I doing wrong?
Thanks for all the help. Any review comments would be appreciated too!
Cheers
Am I successful in doing that? Can I really not access the object attributes?
Indeed. You don't have object attributes, you have local variables in the roverObject function. Local variables can't be accessed from outside, only from the functions inside the roverObject function that have a closure over them.
That you are calling roverObject as a constructor, with new roverObject, is irrelevant, as you are returning a different object from the function. Saying var rover1= roverObject() without the new would do exactly the same thing. Notably the object returned by [new] roverObject is a plain Object as you created it from {}; rover1 instanceof roverObject is false.
If you wanted instanceof to work, you would have to call with new, and use this instead of newRover in the constructor function.
If I want to inherit this object, I should do a newObject.prototype = roverObject will that work? And will that make sense most of all.
No. You currently have no allowance for prototyping. You are using a separate copy of each method for each instance of the roverObject. You can do certainly objects this way but it's a different approach than prototyping. If you wanted to make something like a subclass of roverObject in the arrangement you have now, you'd say something like:
function AdvancedRover() {
var rover= new roverObject();
rover.doResearch= function() {
return rover.where()+' and is doing advanced research';
};
return rover;
}
Note since the ‘private’ local variables in the base class constructor really are private, even the subclass cannot get at them. There's no ‘protected’.
newRover.where = function(){ ... }();
What's that trying to do? I can't get the error you do; all the above does is assigns the string with the location to where (before the setter methods have been called, so it's full of undefineds).
Is there a better way to create this kind of object?
Maybe. see this question for a discussion of class/instance strategies in JavaScript.
Q1: you can create 'private' members in javascript 'classes'. In javascript, privacy is not determined by any access specifier. Instead, access needs to be specifically instrumented. Example:
function MyClass() {
this.val = 100; // public;
var privateVal = 200;
function getVal() { return this.val; } // private method;
this.getPrivateVal = function() { // public method, accessor to private variable
return privateVal;
}
}
Object scope in javascript is governed by a queer concept called closures. AFAIK, there is no parallel concept in any other popular launguage like C+/Java etc.
While I understand what closures are, I cannot put it in words. Perhaps a demonstration will help you:
function closureDemo() {
var done=false;
function setDone() { done=true; }
doLater(setDone);
}
function doLater(func) { setTimeout(func,1000); }
closureDemo();
now, while setDone is called from within doLater, it can still access done in closureDemo, even though done is not in scope (in the conventional procedural sense).
I think you will understand more when you read this.
Q2: I can only say what I do; I don't know if it is better or not. If I wrote your code, it would look like this:
function RoverObject() {
var newRover = {}; // privates
var name;
var xCord;
var ycord;
var direction;
this.setName = function(newName) {
name = newName;
};
this.getName = function() {
return name;
};
this.setDirection = function(newDirection) {
direction = newDirection;
};
// and so on...
this.where = function(){
return "Rover :: "+ name +" is at Location("+xCord+","+yCord+") pointing to "+direction;
};
}
var rover1 = new RoverObject();
Points to note:
capitalization of "class name"'s first letter
use of this instead of roverObject
this function is a pure constructor. it returns nothing.
Q3: if you want to do inheritance, then my method (use of this) will not work. Instead, the public methods should be a part of the prototype of RoverObject. Read this. Excellent material.
Hope that helps.
EDIT: There is a problem with the way your code is doing work. Problems:
your function does not do what its name suggests. Its name had better be createRoverObject, because that's exactly what it is doing. It is not working like a class constructor
the methods supported by your class are part of the object, but the data members are not. While this may work (and it is not, as your console.log() problem suggests), it is not a good way to implement a class in javascript. The problem here is of closures. Again, i'm unable to articulate what the problem specifically is, but I can smell it.
With regards to 4. - you are trying to log the function, not the result of calling the function. Should be console.log(rover1.where()); My guess firebug(I assume it's firebug's console.log) does not like to log function definitions.
EDIT Oh I get it, you are actually executing the where funcion when you assign rover.where. Are you trying to get what looks like a property to actually be a function? If that's the case it won't work. It will have to be a function if you want it to be evaluated when it's called.
What happens in you case where gets executed in the constructor function. At that point you are still creating the roverObject closure and hence it's too early to access it's private variables.
This is just addressing point 1 of your post.
Here's a good article on javascript private members and more:
Private Members in JavaScript
Defining your object like this gives you private members.
function RolloverObject() {
var name;
var xCord;
var ycord;
var direction;
this.setName = function(newName) { name = newName; };
this.getName = function() { return name; };
this.setDirection = function(newDirection) { direction = newDirection; };
this.getDirection = function() { return direction; };
this.setXCord = function(newXCord) { xCord = newXCord; };
this.getXCord = function() { return xCord; };
this.setYCord = function(newYCord) { yCord = newYCord; };
this.getYCord = function() { return yCord; };
this.where = function() {
return "Rover :: " + name + " is at Location(" + xCord + "," + yCord + ") pointing to " + direction;
};
}
var rolloverObject = new RolloverObject();
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();