Durandal 2.0 Widget Disposal - javascript

How is one supposed to properly dispose of a widget in v2.0? From what I have read this is supposedly done automagically when removed from the DOM, but removing my widget from the DOM using say jQuery.remove() doesn't cause canDeactivate() or deactivate() to be called. Is there a specific way it has to be removed from the DOM for the deactivation callbacks to be called?

Yes, in fact there is, and it's kind of easy to miss because it isn't documented very well.
Knockout has a utility function ko.utils.domNodeDisposal.addDisposeCallback(element, callback). This function makes sure the callback is invoked when the element is disposed of. However, 'disposed of' is very specific in this case. jQuery.remove() won't trigger it. The way to dispose of the node is to use ko.removeNode(element), which not only removes the DOM element (and its children), but also does some extra cleanup in terms of bound event handlers and such. (I'm sorry, the details are a bit hazy. You can always check Knockout's implementation if you want more detail on this.)
Internally, when disposing of a view, Durandal uses ko.removeNode. Therefore, when a view is removed, all elements are removed as well and any disposeCallbacks set up using the aforementioned utility function will be invoked. I'm fairly sure that Durandal hooks into this process to trigger the callback for deactivate.
TL;DR: try ko.removeNode(element) instead of jQuery.remove(element). That will trigger your deactivate callback.

Related

Custom Attribute attached event too early?

The custom component
I've created a custom component for the navigation of my app. It consists of an ul element and all its li elements are dynamically created based on the items in the router's navigation list. This is happening in the attached event of the component. Nothing special is going on here.
The custom attribute
But because I want to have a good looking fancy menu I also created a custom attribute and implemented it into the root ul element of the custom component. In the attached event of the custom attribute I'd like to do some dom manipulations so that my menu looks like a menu created by those cool kids.
The problem
Although the attached event of the custom attribute is fired AFTER the attached event of the custom component, the dynamically created li items are not part of the dom in the attached event of the custom attribute yet.
The question
My assumption was that on attached event the view of the actual component is attached to dom and that all components before are also attached to the dom. And when I am done with the attached event the html that has been dynamically created here is also attached. Am I mistaken?
On a side note
I am aware of using TaskQueue could solve my problem. However, I would like to know if there's a different approach/solution first because I believe that moving things in time could cause a chain of paradoxes leaving you in a maintenance nightmare.
Allow me take away your misconception about the TaskQueue.
Your idea of moving things in time causing maintenance issues would certainly apply to using setTimeout() because that incurs an actual delay, and forces execution onto the next event loop. queueTask() is more or less the same thing (it uses setTimeout() internally).
However, the TaskQueue's queueMicroTask() method works very differently.
When you call queueMicroTask(), unlike queueTask() and setTimeout(), the task is scheduled for immediate execution on the same event loop. This is a very robust mechanism with a guaranteed execution order, and it's generally considered good practice to use it within attached() before doing any DOM manipulation.
In fact, queueMicroTask() is used internally by Aurelia in various places (mostly in binding and templating-resources). Two notable places are:
Property- and collection observers use it to "delay" notifying subscribers until all other bindings have completed their internal updating work
The repeat attribute uses it to set an ignoreMutations flag (and unset it after the queue is flushed) to prevent infinite recursion while updating its inner collection
You can generally consider there to be two "phases" to the bind() and attached() hooks: a non-queued, and a queued phase. The queued phase is when components do work that relies on the whole component graph to first be done with some other (usually recursive) process.
queueMicroTask() does not delay execution, just pushes it to the end of the call stack
It's the functional equivalent of passing the function as a callback to the end of the call stack, but saves you the trouble of writing the spaghetti code required to locate that last call and wire it all up. It's super clean.
all its li elements are dynamically created based on the items in the
router's navigation list. This is happening in the attached event of
the component
See, whenever you create anything during attached(), you can't rely on that thing being there during another component's attached() as this depends on the order of compilation/composition. That's an internal matter. This is especially true for custom attributes. Custom attributes (particularly those in style libraries) use the TaskQueue all over the place because it's the only way they can rely on the DOM being done.
Using queueMicroTask() here will guarantee two things:
It's executed when aurelia is completely done with the "first pass" of attacheds and rendering
It's executed immediately when aurelia is done with that - not even a microsecond delayed.
The best (and perhaps only correct) way to address this is indeed by using the TaskQueue - I promise :)

Alternative to Falsely Triggering an Event

TLDR Below
JS Fiddle To Demo
I've been really involved in recreating the tools that are foundations of premiere JS Libraries to better improve my skills. Currently I'm working on functional data-binding a la Angular.
The idea of data-binding is to take data and bind it to elements so that if manipulated all elements subscribed will change accordingly. I've gotten it to work but one thing I hadn't considered going into it was the issue with innerHTML vs value. Depending on the element you need to change one or the other( in the demo above you'll see that I needed to specifically single out the button element in a conditional statement because it has both, but that's kind of a fringe case )
The issue is that in order to capture a SPAN tag update I needed to trigger an event to happen, and the easiest one to manipulate for Text Boxes/Textareas was 'keyup'.
In my function then, if you pass in an element with no value property we assume you're going to be updating innerHTML, and we setup an observer to determine if the element ever mutates, and if it ever does, the observer will emit a 'keyup' event.
if (watchee.value == void(0)) {
var keyUpEvent = new Event('keyup');
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
watchee.dispatchEvent(keyUpEvent);
});
});
observer.observe(watchee, {
childList: true
});
}
Now it may just be my paranoia, but it seems like I might be tunneling into a can of worms by faking 'keyup' on an element that doesn't natively have that support.
TLDR:
I'm curious if there's an alternative way to make, a.e. a span tag reactive other than faking a 'keyup'/'keydown'/'change' event? For instance, is there a way that I can make my own pure event(by pure I mean not reliant on other events) that checks if innerHTML or value has changed and then performs a function? I know that this is probably possible with a timer, but I feel like that might hinder performance.
EDIT: just an aside. In the demo the function called hookFrom works by taking a DOM node and returning a function that will take the receiving dom node and continues to return a function that will take additional receiving dom nodes. :
hookFrom(sender)(receiver);
hookFrom(sender)(receiver)(receiver2);
hookFrom(sender)(receiver)(receiver2)(receiver3)(receiver4)...(receiver999)...etc
JS Fiddle To Demo (same as above)
There is nothing inherently wrong with creating a similar event on a DOM node that doesn't natively have that functionality. In fact this happens in a lot of cases when trying to polyfill functionality for separate browsers and platforms.
The only issue with doing this sort of DOM magic is that it can cause redundancy in other events. For instance the example given in this article: https://davidwalsh.name/dont-trigger-real-event-names shows how a newly minted event using the same event name can cause problems.
The advice is useful, but negligible in this specific case. The code adds the same functionality between text boxes, divs, spans, etc... and they are all intentionally handled the same way, and if the event would bubble up to another event, it would be intentional and planned.
In short: There is a can of worms that one can tunnel into while faking already explicitly defined event names, but in this case, the code is fine!

Kendo - can two Observable objects use the "change" event on the same page?

I have a page that uses a Kendo MVVM approach for two different elements, one providing file search results, the other a document upload facility.
The problem I am encountering is to do with the change event that both elements use - it seems that when one control fires a change event it is then picked up by the other control, which then attempts to process the event and passes it on, at which point it is picked up by the second control's change handler which processes it and passes it on to the first control's change handler. As you might expect, after around 1500 repetitions of this cycle, I see a Uncaught RangeError: Maximum call stack size exceeded message as the JavaScript engine runs out of memory.
At first I thought the problem was that the container of the second model was contained within the first, but even if they are completely separate on the page it seems as though the problem still shows up, so now I'm wondering whether the problem is related to the event being global to the page.
It seems that anything I do in my event handler in terms of trying to stopPropagation or stopImmediatePropagation - or even to set the event to null altogether - makes no difference to this behaviour. Tracing the call stack I can see it looping through Kendo's trigger call then through the event binding on my object and jQuery's dispatch loops that lead it back to Kendo, where it triggers the event handler on the other observable object.
Removing my bindings does not affect the problem, the change event is still bounced back and forth between Kendo and jQuery in the same way, it just doesn't run through my code.
The answer here was not a direct consequence of Kendo itself, so it would have been hard to answer from the question as I set it.
Inside the Observable container that was raising this error, I was using Isotope for layout. The step I had missed was that I had a relationship like this:
Parent [Observable]
-> Container
-> Child
-> Child
-> Child
One of the things that Isotope brings to the party is that for each item in the child collection, it adds a reference to its parent object.
When the child is Observable that creates a structure like this:
Parent [Observable]
-> Container <--┐
-> Child ---|
-> Child ---|
-> Child ---┘
This is an ideal situation for events to be propagated from child to parent, but because the properties in question were being automagically added by the libraries in question it was very hard to troubleshoot.
The solution was to remove the Container layer from the Observable model - it didn't need to trigger anything on change and so I wrapped it in a simple getContainer() closure and used that everywhere I was previously using it as a property. This protected it from the Observable object, breaking the circular reference without harming the functionality.
It may also be relevant that as far as I can tell the initiating event was a DOM change event rather than one of Kendo's own events. The problem may have been avoidable by using a custom Kendo namespace but that would have been a significant change in a complex application and guaranteed to cause a lot of side effects.

Pause jQuery ready events until multiple HTML DOM updates are finished

I am using jQuery to make AJAX submits and receive JSON replies containing multiple DOM IDs and corresponding HTML fragments that I need to update. Thus, I do multiple jQuery.html calls like $('#id1').html('...'); $('#id2').html('...');.
For every fragment containing a ready handler like $(function(){...});, the event is immediately triggered. I'd prefer to call it once after all updates were made.
Is there any way to do that?
From what I've read so far, a jQuery.trigger() could be used to manually trigger the ready event. But I'd need to save and restore the current handlers or postpone event delivery by overwriting the jQuery internals somehow. The latter is something that I'd like to avoid, maybe there's some best practice I don't know yet?
Have a look at the holdReady function.
See: http://api.jquery.com/jQuery.holdReady/
I would start by moving the js you have in your views into external js files where they can be invoked from the ajax callback functions.
As you are finding out in-page ready events can soon leave you feeling out of control and become very hard to maintain. Regain control, namespace your js up into logical sections and lose the ready reliance.
There is no need for ready statements if you include your js before the closing body tag. The best advice I can give is to start being explicit in your apps lifecycle about what js gets called when, rather than relying on the well over abused ready statement.
Rebecca Murphy has written some very good articles/presentations about this.

necessary to remove event handlers by hand?

Morning,
When using Element#observe(), is it necessary to call Element#stopObserving() to completely get rid of the event handler?
Or will some inbuilt mechanism realize that the handler is no longer necessary when the Element gets removed in any way (.update() on a parent, not just .remove()) ?
Updating large dynamic lists with several bindings per entry every now and then. Drawbacks when using something like
ul.update(''); data.each(..
ul.insert(X); X.bind(..); ..);
Thanks!
If an element is no longer part of the DOM then garbage collection will probably deal with it's handlers, but that will depend on the browser.
I would suggest you not worry about what is out of your control and look at using Event.on() instead.

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