Alpine: Alpine.clone results in click handler being called twice

[dvic]

Reported in https://github.com/phoenixframework/phoenix_live_view/issues/1140 with an example repo.

Short summary: I have a list view that gets three items added after 1 second. Each list item has a @click handler. The weird thing is: it seems that Alpine.clone results in the click handler of the list item being called twice. If I remove that line in app.js, the click handlers still work and they are just called once. Also putting x-data on the list item affects this bug, with it, it never gets called twice.

I tried to isolate the issue with a JavaScript only example, but I was not able to (because in that example I'm not calling / don't need to call Alpine.clone). I'm not sure what a "proper" javascript-only example would be that tests whether Alpine.clone is doing the right thing. Any suggestions?

update: the problem is not specific to Phoenix, the problem also exists with Livewire: https://github.com/dvic/hello-livewire (click on the button on the home page, then on the list item, console.log will be called twice)

[dvic]

update I managed to reproduce the issue, not sure if it makes sense though (with the Alpine.clone call):

https://jsbin.com/zucomuguza/1/edit?html,js,console,output

[HugoDF]

From debugging the source it seems that the li listener (technically initializeElements) is getting initialised twice, once by the mutation observer and once by the existing ul component re-initialising itself on post-DOM-insertion

[dvic]

@HugoDF Thanks for looking into it. Is the mutation observer attached to each scope? Because if I remove the x-data on the outer div, the problem disappears.

[KevinBatdorf]

Chiming in again after some thought. Updated my last response as although I think related, also not related (still probably some optimization could be added the the mutation observer though)

Doesn't Alpine.clone() require the target component to have the x-data attribute to work as expected?

Looking at the tests, and adding ul.setAttribute("x-data", ""); to your example case before the cloning seems to work as expected.

Does that change anything in your actual use?

[dvic]

I'm not sure if the x-data is required. If it is, then I don't know how that would help me (I'm using Phoenix LiveView). In my actual usecase, LiveView calls the onBeforeElUpdated callback with the root div of the component that is being updated (which has x-data in this case). The recommended callback in Phoenix LiveView is:

onBeforeElUpdated(from, to) {
  if (from.__x) {
    window.Alpine.clone(from.__x, to)
  }
},

[KevinBatdorf]

Maybe elsewhere too, but I know there is a check in the mutation observer for that x-data attribute, so it's required for some functionality at least.

Can you reproduce the issue on jsbin with the x-data attribute in place?

To solve your main issue though, do you need to use .clone()? Usually there are better ways to do things than rely on the internal API. If you reinsert any Alpine component into the DOM it will re-evaluate itself automatically, for example. Something like $el.replaceWith($el.cloneNode(true)) would be a way to instruct Alpine to reset the component. It depends on your situation though.

[dvic]

Can you reproduce the issue on jsbin with the x-data attribute in place?

No I can't, I'll see if I can come up with other examples but with this one I can't reproduce it.

To solve your main issue though, do you need to use .clone()? Usually there are better ways to do things than rely on the internal API. If you reinsert any Alpine component into the DOM it will re-evaluate itself automatically, for example. Something like $el.replaceWith($el.cloneNode(true)) would be a way to instruct Alpine to reset the component. It depends on your situation though.

Well I'm starting to ask myself the same thing now, I just followed the advice that came out of the suggestion of @calebporzio (https://github.com/phoenixframework/phoenix_live_view/issues/809#issuecomment-632366710 and https://github.com/phoenixframework/phoenix_live_view/issues/809#issuecomment-637671803). I'm not sure why and when the clone() call is necessary, because without it, the particular Phoenix LiveView autocomplete that I have now works. But I (and other users) encountered also situations where it was required to call it, so I'm a bit confused as to whether this is the right way to do it.

[SimoTod]

You need clone to preserve the datacontext between partial renderings, for example you have an x-model that you change. Foralpine, that snippet of html is a new component every time and it would reset to the original x-data content. If you don't need to preserve client side data, you can safely skip clone. It's definitely a bug though.

[dvic]

Clear, and of course with frameworks like LiveView or LiveWire you have one global "onElUpdated" callback so you'd always call clone(), even if you don't need it for a particular element.

[dkln]

I'm having this problem when using LiveView, Alpine and the clone function. What I've noticed, is that after clone, the click listener is still bound to the "old" element. So I end up with two click dispatches with only one being bound to the new DOM element.

[KevinBatdorf]

@dkln Is the old element still on the page? If not, the browser's garbage collector should be clean that up old event listener soon enough, probably after the first click.

[dkln]

Using the Chrome inspector with a little help of a simple console.log reveals that one element is one the page in the DOM and the other one is nowhere to be found. I added this console.log in the click event. This will result in the following:

If I collapse both elements, I see that the invisible element has different contents that it's visible counterpart:

(In the screenshot above, the last log entry is the element that is currently visible on the page)

[dvic]

I think, if I'm not mistaken, that I mimicked exactly this behavior (of Phoenix LiveView) in the above jsbin (https://jsbin.com/zucomuguza/1/edit?html,js,console,output). The main take away that I got from it is that the problem only occurs if the parent is an Alpine container (i.e., has the x-data attribute). I assume this is also the case for you @dkln ?

[dkln]

@dvic correct!

[KevinBatdorf]

What happens if you click a second time? Are both logged again?

[KevinBatdorf]

Okay, I figured why the issue occurs and a solution. However, it's not a trivial fix by any means so I don't think it's something that will be merged in without more examples of it breaking, and without more people coming here with similar issues (Just my guess though!).

Here's the fix implemented with the jsfiddle from before: https://jsbin.com/rakovuruwi/edit?html,js,console,output

_(Note that it's a rough fix and other Alpine tests are failing. Its because it would require a significant refactor and I just wanted to test my thoughts on the current issue here. In short, don't use the code I shared as it's broken in almost every other way than with a simple click event listener)_

@dkln Is it possible to share your code as well?

Best case there is a better way to implement Alpine into LiveView without having to change anything. For example, the fiddle above also works on current Alpine version if you use .cloneNode() to create the new element instead:
https://jsbin.com/bixidewete/edit?html,js,console,output

[dvic]

Haven't looked at the solution, but nice 👍 The cloneNode 'fix' is interesting but I'm not sure it helps because afaik Phoenix LiveView uses https://github.com/patrick-steele-idem/morphdom to update the DOM, maybe I can cook up a reasonable example using morphdom + alpine.js? (if that helps better determine the importance of this issue?)

[KevinBatdorf]

maybe I can cook up a reasonable example using morphdom + alpine.js?

Livewire is using a modified version of morphdom but if it breaks in both versions then a fix should be added so that Livewire is fully supported. If you can reproduce something in Livewire that would be the most ideal, of course.

[dvic]

@KevinBatdorf I can confirm the problem also exists in Livewire (using CDN Alpine 2.7.3), here is an example repo: https://github.com/dvic/hello-livewire

From the console:

This means that the bug is not specific to Phoenix LiveView or Livewire, but probably to this "specific" usage of Alpine + Morphdom?

[dvic]

@KevinBatdorf you mentioned the fix for this issue is not really a trivial fix. Now that we know the bug is also present in Livewire, do you believe there is enough justification to further explore your solution and merge that? Or would you go another direction? If there anything I could help out with, then let me know! Thanks!

[KevinBatdorf]

I just need to find the time to set it up. I might have some time tomorrow actually. Can you mention the steps to reproduce the issue? ie. Load the home page, click the button, etc.

Or is it pretty obvious?

[dvic]

It's the same kind of example, right on the home page of the example app. Good luck!