1143769 - [Customizer] Custom elements are registered multiple times

Status: RESOLVED FIXED

(Firefox OS Graveyard :: Gaia, defect, P2)

Description

[Doug Sherk (:drs) (inactive)]

Add-ons inherit everything from the app that they're injected into, and we're registering some web components from the Customizer. Thus, we sometimes run into situations where the app has registered a web component, and then we attempt to register it a second time from within our add-on code.

Unfortunately, the only way to detect whether or not a web component was already registered is to attempt to register it, and then either catch an exception if it was, or not if it wasn't.

Short-term strategy:
For now, let's just silently ignore duplicate `document.registerElement()` calls. This can be done by commenting out this line:
https://dxr.mozilla.org/mozilla-central/source/dom/base/nsDocument.cpp#6180
I will land a patch for this on cypress after bug 1133943 lands on m-c.

Long-term strategy:
I don't have a very good solution here, but I have some suggestions, sorted in descending order of my preference, without too much thought put into this:
* Augment the web components API to allow us to check whether or not a web component exists. With this, we could just avoid registering it if it's already registered.
* Write some kind of wrapper for all of our web components, perhaps part of our gulp build, that adds some code that catches this particular exception and ignores it.
* Add code to each and every web component to catch exceptions on registration and discard them.

Comment 1

[Wilson Page [:wilsonpage]]

Thinking a try-catch within gaia-component.js might be the best way to deal with this. There are some alternatives [1] but I fear they may pose a greater performance penalty.

[1] http://stackoverflow.com/questions/27334365/how-to-get-list-of-registered-custom-elements

Comment 2

[Doug Sherk (:drs) (inactive)]

I went ahead and landed this change in each component that we're using.

https://github.com/gaia-components/gaia-header/commit/b61a86c71980c93fcaad4b2c53306938be353215
https://github.com/gaia-components/gaia-dialog/commit/38bd55b56093c907cba5b9e54de058f47bfb6ed6
https://github.com/gaia-components/gaia-component/commit/b42cdf4f1866e39db1174aacf50c6119e9133ab9

These changes were really trivial so I didn't ask for review, but I'd be happy to make any followup changes if you'd like, Wilson.

With these changes and a few Gecko patches, the Customizer actually injects into apps and runs. So unless there's any followup work here to be done, I think we can close this bug.

Comment 3

[Wilson Page [:wilsonpage]]

Thanks for this :)