I have a case i hadn't formerly, and really can't figure it out, what is the problem. :(
I tried to make a controller class for my old, unsettled js code, tried to make it a bit more object oriented (aye, fail for me, but practicing also is the mother of knowledge).
So, here is my code:
A function calls Main function, which handle variables and pops a form, like:
function Main(com, multiple, grid) {
if (CheckTableFunctions(arguments) == true)
{
var partner = Partner.Factory(com);
switch(com)
{
case "CreatePartners":
...
break;
case "GetPartners":
$e = ShowModal(); // <- this makes a form visible
Communicate(com, partner, function(data) <- ajax req. with callback
{
... // <- manipulate data, fill form, etc.
});
Main("EditPartners", multiple, grid); // <- calling Main Editpartners case
break;
In fact, the GetPartners case is before the EditPartners, but it is just for fill a form. The Edit, and the event binding goes to editpartners, as seems below:
case "EditPartners":
$e = GetModal(); // <- THE ERROR
$e.find("a.submit").click(function(e){
partner.fx_data.partner.data = getFormData($e)
Communicate(com, partner, function(data) // <- return the modified values by ajax
{
CloseModal();
});
});
break;
So, when i run the fn GetModal it returns with an empty object, but the function works correctly GetModal = fn(){$e=$(".poppedModal");return $e;} after the Main(EditP) runned. I think it's more logical or methodical error than anything else. And to tell the true, i called it with callback, which means i used ShowModal(callback) and when it was ready, i called Main(EditP), but did not work also.
Edit:
Sorry, i forgot the main problem (what i think is the main problem). So i don't have the form exactly i just have a html prototype of it. Prototype, because i always clone it when it needy.
So here is the showmodal fn and i think this makes the modal unreachable:
function ShowModal()
{
$container = $('#myModal');
$clone = $container.clone();
$clone.removeAttr("id").addClass("clonedModal");
$clone.modal('show');
return $clone;
}
function ShowModal()
{
$container = $('#partnerModal');
document.getElementById('partnerForm').reset();
$container.modal('show');
return $container;
}
Thanks for your help.
Répás
Several points:
Members within javascript functions are only localised if declared with var. Otherwise they are 'outer' members up to and including the global name space. Several of your vars need to be localised. Undeclared vars can result in nasty bugs.
.clone() will indeed create a clone of an DOM fragment but does not automatically inert it back into the DOM. You need to do that with jQuery instructions such as .append(), .prepend(), .before(), .after(). I strongly suspect that a large part of your problem is trying to do .modal() on an uninserted clone.
It's not clear why the form needs to be cloned each time it is used. This sort of programming is likely to cause memory leaks. It would be cleaner and more normal to reuse a single form. It's not hard to reset a form to clear out previously entered/selected values.
EDIT:
ShowModal with properly localised variable :
function ShowModal() {
var $container = $('#partnerModal');
document.getElementById('partnerForm').reset();
$container.modal('show');
return $container;
}
In fact, if .modal() is written to be chainable, as it should be, then ShowModal() can be simplified to avoid creating any named members, local or otherwise :
function ShowModal() {
$('#partnerForm').get(0).reset();
return $('#partnerModal').modal('show');
}
Also, please note that, by convention in javascript programming, only constructor functions should be named with an initial Capital. Constructor functions are those designed to be called with new Fn(). (It's not important here but there has been much discussion on the subject of constructors and some choose to write their code to avoid the use of new).
Related
Coming from a C++ background, trying to work with an OO language that doesn't have explicit typing is a little more than a headache.
So I have dynamic elements for a webpage that are "controlled" by objects since there are tons of stuff I need to manage on each for it to work. The element is just the visual output of the data inside of the object itself, that's all I really need it for.
Except that I need the object to perform an internal function when it's clicked. That seems to be the biggest source of my headache thus far.
Javascript:
function onClick(file) //The external onClick function I use to try to get it to call from.
{
file.state = INUSE;
file.checkState();
}
function fileObject () { //The file object itself
this.element;
this.newElement();
//initialize stuff for the object
}
fileObject.prototype.newElement = function() { //creates a new element and sets its event listener
this.element.click(function() {onClick(this)});
}
fileObject.prototype.checkState = function() {/*does stuff*/} //apparently this is "not a function"
The error I get exactly is "file.checkState is not a function" from Firefox's console panel.
I'm still new to javascript, but after doing some debugging, I've come to find out that it's explicitly the onClick(this) function that is causing all of the errors. When used with something else, the onClick function works perfectly, but for some reason, the this keyword doesn't appear to actually be sending the reference to the fileObject since all checks show file being undefined when inside of the onClick scope.
Is there something fundamentally wrong about the way I'm trying to do this or am I just missing a step (or adding something that I don't need) that will help get this snippet working.
So you know, your initial problem isn't actually handling the action, but listening to it. click will trigger a synthetic click event, rather than liste for one.
You want ... .element.addEventListener("click", callback); that said, you face a second problem, immediately thereafter.
I will leave my example code as you've written it to not confuse the matter...
But when you see click( ) know that I mean subscribing with addEventListener, if element really does mean a browser DOM element. If it's not a standard browser element, and your own API, then ignore the previous portion, and carry on.
this is dynamically bound at the invocation time of the function (not at definition time).
The nearest function, scoped above, is your callback function that you are passing into .click( ... ).
Which is entirely different than the this which you mean outside of the callback.
Whatever is on the left-hand side of the dot is the this context for the duration of that particular invocation.
Needless to say, click() doesn't know enough to bind the this you mean, to the left-hand side of your callback.
The solution (or one of many) is to use lexical scoping and/or closure to retain the value of the object you mean.
// easy but messier
var fileObject = this;
... .click(function () { onClick(fileObject); });
// Cleaner with thunks:
function clickHandler (onClick, obj) {
return function () { onClick(obj); };
}
... .click(clickHandler(this));
Coming from c++ the way Javascript handles this will seem a little crazy, it looks like here you need to tell the function you've defined what this is - like so:
this.element.click(function() {onClick(this)}.bind(this));
Let's say I'm creating a chat system in javascript.
var ChatController = function() {
this.receiveMessageInteractor = new ReceiveMessageInteractor(this);
// ReceiveMessageInteractor delegate
this.didReceiveMessage = function(message) {
// ...
};
};
The ChatController also does some other stuff related to creating the html for the messages, but that's not important here.
The ChatController sets himself as a delegate of the ReceiveMessageInteractor, which will call the didReceiveMessage when a new message arrives.
var ReceiveMessageInteractor = function(delegate) {
this.observer = NotificationCenter.addObserver('DidReceiveMessageNotification' , function(data) {
var message = data['message'];
// format some message data
delegate.didReceiveMessage(message)
});
};
The ReceiveMessageInteractor just subscribes to a notification (NotificationCenter here is similar to the iOS one), does some formatting with the data and passes a message object to the delegate;
When the chat view goes of the screen (html gets deleted), my MenuController stops holding a pointer to ChatController, in which case I'd like it to be deleted, along with ReceiveMessageInteractor and observer.
The problem is that Javascript has no weak references, so ReceiveMessageInteractor is holding a pointer to ChatController, and even if ChatController wasn't holding a pointer to ReceiveMessageInteractor, my ChatController would still be alive, because the notification callback is holding a pointer to it (delegate).
So even if ReceiveMessageInteractor stopped existing, my ChatController would still not go away when the MenuController stops holding a pointer to it (because I can't have a weak reference inside the notification callback).
How do I solve this problem?
How do I solve this problem?
By understanding JavaScript. The problem is not that "Javascript has no weak references", the problem is that you don't know how to work without them because you come from a language that has them.
How would you remove that reference in any other language that doesn't have weak refs natively? Let's say C++. You would do like everyone does, including the implementors of the compiler/garbage collector/weak refs you're used to: you clean up after yourself.
function ChatController() {
this.receiveMessageInteractor = new ReceiveMessageInteractor(this);
// ReceiveMessageInteractor delegate
this.didReceiveMessage = function didReceiveMessage(message) {
// ...
};
this.destroy = function destroy() {
this.receiveMessageInteractor.destroy();
};
};
function ReceiveMessageInteractor(delegate) {
function callback(data) {
var message = data.message;
// format some message data
delegate.didReceiveMessage(message);
}
this.observer = NotificationCenter.addObserver('DidReceiveMessageNotification', callback);
this.destroy = function destroy() {
// Or however you NotificationCenter works, I don't know
NotificationCenter.removeObserver('DidReceiveMessageNotification', callback);
};
};
The Observer pattern implies resource management, even though it's not obvious (how is an "observation" relationship a resource??). Acquire and release. No hand-holding.
Also, notice the change in style. And please, learn the language, use prototypes, and, although not everyone will agree with me on this point, do not assign methods in the constructor.
edit: I forgot to add: ReceiveMessageInteractor? Really? What's wrong with MessageReceiver or something in that vein?
Your problem is not with the absence of weak references. All of your objects continue to have a hard reference, all originating from your NotificationCenter.
The NotificationCenter has a reference to the data handler, which has closure access to it's parent ReceiveMessageInteractor instance, as well as access to the delegate variable. Removing a reference to delegate from elsewhere won't break the anonymous function's access to it, therefore it stays.
What you'll need to do is add a .cleanup() method to each Controller that is called when it is removed.
In the ChatController.cleanup() method, you would want to call a method to remove the observer, something along the lines of this.receiveMessageInteractor.observer.unsubscribe().
The .unsubscribe() method should be defined in the NotificationCenter and remove the function(data) { ... } method you defined in .addObserver() from whatever data structure is holding it (or further down the line).
This is the same kind of pattern Facebook utilized in it's React framework + Flux architecture. Each component has a componentWillUnmount() method that assists in cleaning up data event handlers just like yours.
I have tried searching through a lot of S.O. pages but nothing has touched EXACTLY on this top while also NOT USING JQUERY.... I am trying to stick to pure JavaScript as I want to learn it 115% before advancing my current knowledge of JQuery.
I have an object called ScreenResizeTool like this...
function ScreenResizeTool(currImg) {
window.addEventHandler('resize', function() {
listen(currImg);
}, true);
}
and a method like this...
ScreenResizeTool.prototype.listen = function(currImg) {
//Random Code For Resizing
};
My trouble is probably obvious to an experienced JavaScript user but I am having trouble not making this into a messy dirty awful OOP set. I have done various tests to show and prove to myself that the this inside the addEventHandler changes when it becomes bound to the window. This much I assumed before testing but I was able to see that once window.resize event happens the listen method is gone and not a part of the global window variable....
I have also tried adding a this capture such as this.me = this inside the object constructor however it also couldn't see the me variable once it ran. Once the window took the function over it no longer knew anything about the me variable or any reference to my class methods....
I am aware that I could separate this differently but my goal here is to learn how to fully encapsulate and use as many clean OOP structures as possible as I just came from the .NET world and I need it in my life.
I am also aware that I could make messy calls and or store this object or access to the methods inside the window variable but that seems outright wrong to me. I should be able to fully encapsulate this object and have its events and methods all implemented in this class structure.
I also know that the currImg variable is not going to be seen either but lets start small here. I assume once I figure out my incorrect train of thought on scope for JavaScript I should be fine to figure out the currImg problem.
I know there's 1000 JavaScript programmers out there waiting to rip me a new one over asking this simple question but I gotta know...
Thoughts anyone?
this inside a function bound to a DOM Object (like window) will always refer to that object.
this inside a constructor function will always refer to the prototype.
A common practice to circumvent the this issue, as you mentioned, is to cache it in a variable, often called self. Now you want the variables and properties of your object available after instantiation, so what you need is the return keyword, more specifically to return the parent object itself. Let's put that together:
function ScreenResizeTool() {
var self = this;
// method to instantiate the code is often stored in init property
this.init = function() {
window.addEventListener('resize', function() {
self.listen(); // self will refer to the prototype, not the window!
}, true);
};
return this;
}
ScreenResizeTool.prototype.listen = function() { // Dummy function
var h = window.innerHeight, w = window.innerWidth;
console.log('Resized to ' + w + ' x ' + h + '!');
};
Pretty easy huh? So we have our prototype now, but prototypes can't do anything if there's not an instance. So we create an instance of ScreenResizeTool and instantiate it with its init method:
var tool = new ScreenResizeTool();
tool.init();
// every time you resize the window now, a result will be logged!
You could also simply store the listen & init methods as private functions inside your constructor, and return them in an anonymous object:
function ScreenResizeTool() {
var listen = function() { ... };
var init = function() { ... };
// in this.init you can now simply call listen() instead of this.listen()
return {
listen: listen,
init: init
}
}
Check out the fiddle and make sure to open your console. Note that in this case I'd rather use the first function than the second (it does exactly the same) because prototypes are only useful if you have multiple instances or subclasses
The whole concept of this in JavaScript is a nightmare for beginners and in my code I usually try to avoid it as it gets confusing fast and makes code unreadable (IMHO). Also, many people new to JavaScript but experienced in object-oriented programming languages try to get into the whole this and prototype stuff directly though the don't actually need to (google JS patterns like IIFE for example as alternatives).
So looking at your original code:
function ScreenResizeTool(currImg) {
window.addEventHandler('resize', function() {
listen(currImg); // global function listen?
}, true);
}
ScreenResizeTool.prototype.listen = function(currImg) {
//Random Code For Resizing
};
First off, you probably mean addEventListener instead. In its callback you refer to listen but as a global variable which would look for it as window.listen - which doesn't exit. So you could think to do this:
function ScreenResizeTool(currImg) {
window.addEventHandler('resize', function() {
this.listen(currImg); // what's this?
}, true);
}
As you want to use the prototype.listen function of ScreenResizeTool. But this won't work either as the event listener's callback function is called with a different this and not the this that is your function scope.
This is where something comes in which makes most programmers cringe, you have to cache this, examples from code I've seen:
var _this = this;
var that = this;
var _self = this;
Let's just use the latter to be able to refer to the function within the event callback:
function ScreenResizeTool(currImg) {
var _self = this;
window.addEventListener('resize', function() {
_self.listen();
}, true);
}
Now this will actually work and do what you want to achieve: invoke the prototype.listen function of ScreenResizeTool.
See this JSFiddle for a working example: http://jsfiddle.net/KNw6R/ (check the console for output)
As a last word, this problem did not have anything to do with using jQuery or not. It's a general problem of JS. And especially when having to deal with different browser implementations you should be using jQuery (or another such library) to make your own code clean and neat and not fiddle around with multiple if statements to find out what feature is supported in what way.
After discovering about Javascript namespaces, I tried to implement them but I run into a problem while trying to attach a namespace method to an element's onclick.
I used this method to wrap up my functions/methods/classes (a simplified concept, not my actual code):
;(function(window, undefined) {
//my namespace
var NS = {};
NS.test = {
f : function(param) {
alert(param);
}
}
NS.test.('test 2');
})(window);
Inside, everything works fine and "test 2" is prompted.
However, when I try to attach that function to a click event, by doing something like this:
<a href-"#" onclick="NS.test.f('test');">Click me!</a>
it doesn't work, just like it doesn't work when I call that function after the })(window); part.
I tried it calling it window.NS.test.f('test'); but with no effect.
How can I make an onclick event call my function?
I could attach an event listener inside my wrapper, like I do for other html elements with no difficulty, but it would be problematic in this case since I'm generating the links with javascript and I find it easier and simpler to just add onclick="doSomething" for all my links, instead of creating them, then cache them and add event listeners.
Call me lazy, but in this particular case I prefer to do
someDiv.innerHTML = my_Generated_Html_Code_With_OnClick;
instead of
//demo code, ignore the flaws and the fact it won't work on IE
someDiv.innerHTML = my_generated_Html_code;
myLink = document.getElementById(id);
myLink.addEventListener('mousedown', NS.test.f('test'));
I do not use any framework nor do I wish to, since I'm trying to get a better understanding of the so-called vanilla javascript first.
I set up a jsfiddle here.
P.S. I must admit I didn't understand namespaces completely so if I'm doing something wrong here or applying the concept in a way I am not supposed to, I would appreciate any tips or corrections
That's because NS is declared inside and hence only exists inside the function:
function(window, undefined) {
var NS = {};
// NS exists here ...
}
// ... but not here
If you want to make it available to the rest of the page, then you can do:
function(window, undefined) {
var NS = window.NS = {};
// NS and window.NS exist here ...
}
// ... and window.NS exists here.
Trying to use an svg onClick to call a prototype function.
Usually to call a prototype function I would just do this.(functionName) but when I put it into the .setAttribute(onclick, "this.(functionName)") it does not recognise the prototype function. Has anyone had any experience in this?
In case the above wasn't clear heres the basic jist of it...
function myobject(svgShape) {
this.svgshape.setAttribute(onclick, 'this.doSomething()');
}
myobject.prototype.doSomething = function() {
alert("works");
}
Three things that may help:
1) First off, I think you're missing this line from the top of your myobject function:
this.svgshape = svgshape;
I'm assuming that was just an error posting the question and have inserted that below.
2) Normally when you're using Prototype (or any modern library), you don't use strings for callbacks, you use functions. Also, you normally assign handlers using the library's wrapper for addEventListener / attachEvent (observe, in Prototype's case) rather than the old DOM0 attribute thing. So:
function myobject(svgShape) {
this.svgshape = svgshape;
$(this.svgshape).observe('click', this.doSomething); // STILL WRONG, see below
}
myobject.prototype.doSomething = function() {
alert("works");
}
3) But JavaScript doesn't have methods (it doesn't really need them), it just has functions, so the above won't ensure that this (the context of the call) is set correctly. With Prototype you'd use bind to set the context:
function myobject(svgShape) {
this.svgshape = svgshape;
$(this.svgshape).observe('click', this.doSomething.bind(this));
}
myobject.prototype.doSomething = function() {
alert("works");
}
(Or you can use your own closure to do it. The advantage of bind is that the closure is in a very well-controlled environment and so doesn't close over things you don't want kept around.)
Now, I've never done any SVG programming with Prototype, so if observe doesn't work for some reason, you might try directly assigning to the onclick reflected property:
function myobject(svgShape) {
this.svgshape = svgshape;
this.svgshape.onclick = this.doSomething.bind(this);
}
myobject.prototype.doSomething = function() {
alert("works");
}
I'm still using bind there so that this has the correct value.
These posts from my anemic little blog offer more discussion of the above:
Mythical methods
You must remember this
Closures are not complicated