This is probably a stupid question, but is there way in Javascript (ES5 preferred) to "extend" a class function similar to how i can i extend a parent' function in PHP ?
Basicly, i have this class hierarchy from System -> Weapon -> Dual and i would like Dual to use the code from System.setState() and then do some more stuff.
Note i use pre ES6 syntax for my hierarchy.
function System(system){
this.setState = function(){
//do stuff
}
}
function Weapon(system){
System.call(this, system);
}
Weapon.prototype = Object.create(System.prototype);
function Dual(system){
Weapon.call(this, system);
this.setState = function(){ // this is the problem
System.prototype.setState(); // error - not defined
//Weapon.protoype.setState() doesnt work either
//do more stuff
}
}
Dual.prototype = Object.create(Weapon.prototype);
Because setState is an instance property of System it does not exist on System.proptotype so you can't call it using System.prototype.setState.call. If you want to call it in this case, just create an object from System like so
function Dual(system){
Weapon.call(this, system);
var parent = new System(system);
this.setState = function() {
parent.setState(); // done
}
}
Instance properties are duplicated on each individual object ( they don't share). Whereas, prototype properties will be shared among children( they are not duplicated on child classes). To make all System 's subclasses share setState function, add it to System 's prototype
function System (arg) { ... }
System.prototype.setState = function () {...}
Now in your child classes, you can do
function Dual(system){
Weapon.call(this, system);
this.setState = function() {
System.prototype.setState.call(this); // done
}
}
First, you should set your instance methods on the prototype:
System.prototype.setState = function() {
// your stuff
}
This will improve performance and allow you to inherit the method without constructing a System instance.
Then, you just need to call System's version of setState on the right object (the instance of Dual) instead of calling it on System.prototype:
Dual.prototype = Object.create(Weapon.prototype, {
'setState': { value: function(){
System.prototype.setState.call(this) // fixed
// other stuff
}}
})
Related
I try to change some way to call methods into namespace.
Calling parent methods (I dont think its possible)
Creating and call inheritance function
Calling inside another method (mostly jquery onReady event function) (this.MyFunction() not working)
I split every namespace in files (want to keep it that way)
I try How to call function A from function B within the same namespace? but I didn't succed to split namespaces.
my fiddle sample got only 1 sub-namespace but could be more.
https://jsfiddle.net/forX/kv1w2rvc/
/**************************************************************************
// FILE Master.js
***************************************************************************/
if (!Master) var Master = {};
Master.Print= function(text){
console.log("master.Print :" + text);
$("body").append("<div>master.Print : " + text + "</div>");
}
/**************************************************************************
// FILE Master.Test1.js
***************************************************************************/
if (!Master) var Master = {};
if (!Master.Test1) Master.Test1 = {};
/**************************************************************************
* Descrition :
* Function for managing event load/documentReady
**************************************************************************/
Master.Test1.onReady = function () {
$(function () {
Master.Test1.Function1(); //try to replace because need all namespace.
try {
this.Function2(); //not working
}
catch(err) {
console.log("this.Function2 not working");
$("body").append("<div>this.Function2 not working</div>");
}
try {
this.Print("onReady"); //not working
}
catch(err) {
console.log("this.Print not working");
$("body").append("<div>this.Print not working</div>");
}
try {
Print("onReady"); //not working
}
catch(err) {
console.log("Print not working");
$("body").append("<div>Print not working</div>");
}
});
}
Master.Test1.Function1 = function () {
console.log("Function1");
$("body").append("<div>Function1</div>");
this.Function3(); //working because not inside another function
}
Master.Test1.Function2 = function () {
$("body").append("<div>Function2</div>");
console.log("Function2");
}
Master.Test1.Function3 = function () {
$("body").append("<div>Function3</div>");
console.log("Function3");
Master.Print("Function3"); //try to replace because need all namespace.
}
Master.Test1.onReady();
I use Master.Test1.Function1(); and I want to change that because Function1 is inside the same namespace.
I use Master.Print("Function3"); I dont think I can change that. the way I try to use it, it's more an inheritance function. but I dont know if theres a way to do that?
Maybe I should change the my namespace methode? maybe prototype will do what I want?
You can capture the this in a variable because this inside $(function() {}) will point to document object. The below will work provided you never change the calling context of onReady -- i.e. it is always called on the Test1 object and not called on other context:
Master.Test1.onReady = function () {
var self = this;
$(function () {
self.Function1();
// ..
});
}
To access Print you have to reference using the Master object like: Master.Print() as it won't be available in the Test1 object
this is document within .ready() or jQuery() alias for .ready() where function(){} is parameter $(function() {}). this at this.Function2() will reference document.
"Objects" in javascript are not built the same way as in most object-oriented languages. Essentially, what you are building is a hierarchy of static methods that have no real internal state in-and-of themselves. Therefore, when one of the defined methods is invoked, the context (or state) of that method depends on what object invoked the method.
If you want to have any internal context, you will need to create an "instance" of an "object prototype". At that point, you can use "this.otherFunction" within your other functions. Here is a small example:
var MyObject = function() {};
MyObject.functionOne = function() {
console.log("Function 1");
this.functionTwo();
};
MyObject.functionTwo = function() {
console.log("Function 2");
};
var instanceOne = new MyObject();
instanceOne.functionOne();
You might get some more information about object definition here
I have a simple requirement, I need add the same code to hundreds of other JavaScript functions, the code can be executed at the end of the function, is there a handy way of doing it, like attach an function to another function dynamically, I think yes, because JavaScript is so powerful and too powerful, any ideas?
Note, I need dynamically assign new code or function to existing functions without change existing function's code, please give a solid solution, I can do it in hacky way, but no hacky way please!
The first method that comes to mind is simply create another function:
function primaryFunction() {
// ...
utilityMethod();
}
function otherPrimaryFunction() {
// ...
utilityMethod();
}
function utilityMethod() { ... }
Now utilityMethod() gets called from the end of each other primary function.
There's also a method which requires more code refactoring but is better in the long term: classes/prototypes.
Essentially, you have one "constructor" function which takes a number of parameters for the "class" and returns an class-like object:
function constructor(someClassField, anotherField) {
this.aField = someClassField;
this.fieldTwo = anotherField;
return this;
}
Now if you call this and pass some parameters, you get a class out:
var myClass = new constructor("1", "2");
myClass.aField == "1";
myClass.fieldTwo == "2";
So: If you define your utility method as above, then you can use this: for every primary function you instantiate a new instance of the constructor, with the final code looking like this:
function constructor(primaryFunction) {
this.function = primaryFunction;
this.call = function() {
this.function();
utilityMethod();
}
this.call();
return this;
}
function utilityMethod() { ... }
var primaryMethod = new constructor(function() { ... });
The creation of primaryMethod now automatically calls the primary function followed by the utility method, before returning the object so you can re-call both if you want to.
This question already has answers here:
JavaScript: Class.method vs. Class.prototype.method
(5 answers)
Closed 9 years ago.
As i read through some examples of Angularjs' UI add-on, i've stumbled over some code that showed me that my knowdledge of Javascript is quite improvable:
The following is a class inside of an Angular provider:
function Dialog(opts) {
var self = this, options = this.options = angular.extend({}, defaults, globalOptions, opts);
this._open = false;
this.backdropEl = createElement(options.backdropClass);
if(options.backdropFade){
// ...
}
this.handleLocationChange = function() {
self.close();
};
// more functions
}
Pretty straightforward. But outside of that class, there are prototype functions, e.g the above invoked close()
Dialog.prototype.open = function(templateUrl, controller){
var self = this, options = this.options;
// .. some code
};
Now i do not understand why that function is declared as a prototype, but handleLocationChange inside the class itself.
How do i decide which method to choose?
The full gist can be found here
Consider these 2 cases:
Dialog.prototype.open = function...
Dialog.open = function....
First case - every object created by calling new Dialog() will have this open function
Second case has nothing to do with dialog objects, consider it as static function.
EDIT
found a great answer here : javascript-class-method-vs-class-prototype-method
function open will be shared by all objects create using new Dialog().. and handleLocationChange will be different for different objects.
I think handleLocationChange is called from event triggering object that registers listeners but doesn't register the this context so when it's triggered you can't use this as it refers to handleLocationChange. To overcome this they have chosen to set a closure reference to this (=the self variable) and call other instance functions using self. Basically it's storing a value known at creation but not known when handleLocationChange is executing.
Here is some code showing the problem:
var eventSystem={
events:{},
add:function(eventname,fnCallback){
if(!this.events[eventname]){
this.events[eventname]=[];
}
this.events[eventname].push(fnCallback);
},
trigger:function(eventname){
if(!this.events[eventname]){
return;
}
var i=0;
for(i=0;i<this.events[eventname].length;i++){
this.events[eventname][i]();
}
}
};
var person=function(name){
this.name=name;
};
person.prototype.sayName=function(){
console.log("this is now:",this.toString());
// logs this is now: function (){ console.log("this is now:...
// so this is now the sayName function not the person instance
console.log(this.name);//undefined: sayName doesn't have a name property
}
var jon=new person("jon");
eventSystem.add("sayname",jon.sayName);//add event and listener function
eventSystem.trigger("sayname");//trigger the event
Here is how it's solved setting a closure reference
var eventSystem={
events:{},
add:function(eventname,fnCallback){
if(!this.events[eventname]){
this.events[eventname]=[];
}
this.events[eventname].push(fnCallback);
},
trigger:function(eventname){
if(!this.events[eventname]){
return;
}
var i=0;
for(i=0;i<this.events[eventname].length;i++){
this.events[eventname][i]();
}
}
};
var person=function(name){
var self=this;// set closure ref to this
this.name=name;
this.sayName=function(){
console.log(self.name);//use closure ref to get this
// logs jon
}
};
var jon=new person("jon");
eventSystem.add("sayname",jon.sayName);//add event and listener function
eventSystem.trigger("sayname");//trigger the event
Here is a fix to the event system to take care of the this context:
var eventSystem={
events:{},
add:function(eventname,fnCallback,thisRef){
if(!this.events[eventname]){
this.events[eventname]=[];
}
this.events[eventname].push({
"callback":fnCallback,//store the event handler
"thisRef":thisRef//store the this context
});
},
trigger:function(eventname){
if(!this.events[eventname]){
return;
}
var i=0;
for(i=0;i<this.events[eventname].length;i++){
this.events[eventname][i].callback.call(
this.events[eventname][i].thisRef);
}
}
};
var person=function(name){
this.name=name;
};
person.prototype.sayName=function(){
console.log("this is now:",this);//referring to person instance
// with the name jon
console.log(this.name);//logs jon
console.log(this instanceof person);//true
}
var jon=new person("jon");
eventSystem.add("sayname",jon.sayName,jon);//add extra parameter for this ref
eventSystem.trigger("sayname");//trigger the event
The pattern used above is not an event system (think it's pulisher subscriber) as an event usually get triggered on or invoked from an object (button, input, dialog) but in case of a more event system like implementation it would be easy to get the correct this context since you trigger the event on or from an instance (like myButton or myDialog).
See following code for event system like implementation:
var eventSystem={
add:function(eventname,fnCallback){
if(!this.events[eventname]){
this.events[eventname]=[];
}
this.events[eventname].push(fnCallback);
},
//change in trigger as it's passing the event object now
trigger:function(event){
if(!this.events[event.type]){
return;
}
var i=0;
for(i=0;i<this.events[event.type].length;i++){
this.events[event.type][i](event);
}
},
initES:function(){//set the instance variables needed
this.events=this.events||{};
}
};
function addProtos(o,protos){
for(item in protos){
o.prototype[item]=protos[item];
}
}
var person=function(name){
this.name=name;
this.initES();//needed to initialeze eventsystem
};
// make person capable of storing event handlers
// and triggering them
addProtos(person,eventSystem);
person.prototype.askQuestion=function(){
//asking a question will trigger an "answer" event
this.trigger({type:"answer",target:this});
}
// handler for when jon will fire an answer event
function answerHandler(event){
console.log("answer from:",event.target);
console.log("name of the person:",event.target.name);
}
var jon=new person("jon");
jon.add("answer",answerHandler);//add event listener
jon.askQuestion();//triggers the answer event from within jon
jon.trigger({type:"answer",target:jon});//trigger the event externally
Not sure why Angular choose to "break" prototype by using closures as the examples show there are other alternatives. Maybe someone can explain that who is more familiar with Angular.
Can anyone tell me why my 'showDiv_boo' is undefined inside the class´s method?
I also can´t access my class´s methods.
Here´s my class 'Blink' class with its properties and methods:
function Blink(div) {
this.div = div
}
Blink.prototype.counter = 0
Blink.prototype.showDiv_boo = true
Blink.prototype.showDiv = function() {
this.div.style.visibility = 'visible'
}
Blink.prototype.hideDiv = function() {
this.div.style.visibility = 'hidden'
}
Blink.prototype.startEngine = function() {
if (this.showDiv_boo) {
this.showDiv()
} else if (!this.showDiv_boo) {
this.hideDiv()
}
this.showDiv_boo = !this.showDiv_boo
this.counter++
}
Blink.prototype.startEffect = function() {
this.idEffect = setInterval(this.startEngine, 1000 / 45)
}
So, if I create:
_blink = new Blink(myDiv);
_blink.startEffect();
You can test... the variable 'showDiv_boo', is undefined inside the method.
Even, if I set the showDiv_boo inside the method to true, it won´t call my class´s methods showDiv or hideDiv.
Anyone?
Thanks :)
The reason why is that startEngine is called from setInterval. The way in which this callback is invoked causes startEngine to have a different value for this than startEffect. You need to save this in order to maintain it in the callback. For example.
Blink.prototype.startEffect = function () {
var self = this;
self.idEffect = setInterval(function () { self.startEngine(); }, 1000 / 45);
};
You need to:
use var self and call the method via self.startEngine()
use an anonymous function to wrap the call in [1] i.e. function(){ self.startEngine(); }
This is because when you just pass this.startEngine or self.startEngine you are just passing the function startEngine without specifying what this is, which in both cases is supplied by the global conext of DOMWindow.
To give an example...
function startEngine() {
...code omitted...
};
Blink.prototype.startEngine = startEngine;
Blink.prototype.start = function() {
setTimeout(startEngine, 0); // obviously wrong, what is this?
setTimeout(Blink.startEngine, 0); // actually the same as line above, although not as obvious
setTimeout(startEngine.bind(this), 0); // works correctly
}
works to add code to the prototype and if used in the anonymous function will work as expected, but if you just use Blink.startEngine as the callback it is exactly the same as using startEngine only the second is more obviously wrong because there's no object it is being called on so you'd expect this to be whatever is supplied by the context.
The other way you could do this without using the anonymous function would be
Blink.startEngine.bind(self)
Which returns a function that will call startEngine with the correct this same as explicitly creating the anonymous function and wrapping the call to self.startEngine()
Heres a link to a fiddle to play around with the differences: http://jsfiddle.net/bonza_labs/MdeTF/
If you do the following, you will find it is defined
var x = new Blink('hello');
x.showDiv_boo
Javascript uses prototypical inheritance. While showDiv_boo may not be explicitly defined within the instance of Blink that you now have, it does exist within the prototype that Blink inherits from. When you try referencing showDiv_boo from within the object, the Javascript engine realizes the object does not own a member by that name and then will check its prototype.
Along with setting a temporal variable to store this, you must call the startEngine() function with that variable:
Blink.prototype.startEffect = function(){
var self = this;
self.idEffect = setInterval(function(){ self.startEngine.call(self); }, 1000/45);
}
Note the .call(self), which basically calls the function with the variable self, so the variable this in startEngine will be the correct one.
I'm quite experienced with jQuery but I'm just getting into object oriented Javascript and want to make sure I'm doing it right.
Here's an example of what I'm doing so far... I'd appreciate tips/advice on how I can improve my approach:
// create a class for collapsable fieldsets
window.CollapsableFieldset = (function() {
function CollapsableFieldset(jQObject) {
// look for all the legend tags within this fieldset
jQObject.find("legend").click(function(event) {
// add or remove the "open" class to the fieldset
return jQObject.toggleClass("open");
});
}
return CollapsableFieldset;
})();
jQuery(document).ready(function() {
return $("fieldset.collapsable").each(function(i, element) {
return new CollapsableFieldset($(element));
});
});
So basically I'm creating a class that defines the behaviour I'm looking for and then in the jQuery block, I'm selecting each object that matches and creating a new instance of the class with that object as an argument.
This is not object-oriented javascript.
Before getting into prototyping, let me make one remark: your use of a closure in CollapsableFieldset is unnecessary and cumbersome. Indeed, you do not have any variables in the (function(){})() pattern. You may rewrite, without any loss, to:
window.CollapsableFieldset = function (jQObject) {
jQObject.find('legend').click(function(event) {
return jQObject.toggleClass('open');
});
}
Now, you create classes in javascript using a function constructor, in which the "this" keyword defines the object that a "new" statement will yield:
function CollapsableFieldset (jQObject) {
// This is the function constructor.
this.field = jQObject;
}
CollapsableFieldset.prototype.findAndToggle = function (tag, cssclass) {
// This defines a method "findAndToggle" on the CollapsableFieldset type.
this.field.find(tag).click(function(event) {
return this.field.toggleClass(cssclass);
});
};
jQuery(document).ready(function() {
return $("fieldset.collapsable").each(function(i, element) {
var colFieldset = new CollapsableFieldset($(element));
return colFieldset.findAndToggle('legend', 'open');
});
});
Please bear in mind that object-oriented javascript is not always the optimal solution.
One option would be to use Jquery UI's widget factory and encapsulate behaviour in widgets.
http://wiki.jqueryui.com/w/page/12138135/Widget-factory
You are using an immediately called function expression for no good reason, your code is functionally equivalent to:
function CollapsableFieldset(jQObject) {
// look for all the legend tags within this fieldset
jQObject.find("legend").click(function(event) {
// add or remove the "open" class to the fieldset
return jQObject.toggleClass("open");
});
}
The "constructor" doesn't return the object created when it is called with new, no advantage it taken of prototype inheritance so no point to using new.
The object returned by the function isn't assigned to anything, so what's the point of returning anything?
> jQuery(document).ready(function() {
> return $("fieldset.collapsable").each(function(i, element) {
> return new CollapsableFieldset($(element));
> });
> });
Where does the object returned by new CollapsableFieldset(...) go?
Incidentally, there is no point to creating global variables using:
window.varName...
when
var varName ...
does it so much better.