Polyfill doesn't work if another script patches the DOM about custom-elements

[joeldenning]

patching functions directly on document is something that I have seen in several codebases (not just LastPass), which has me worried. What are the reasons you prefer patching Document.prototype? Are you worried about other instances of Document besides document? Or is it more just that Document.prototype is the right place to do it?

My thoughts are that a polyfill really can't expect a browser environment to be especially cooperative, and that the code should be defensive so that it works in as many situations as possible. What do you think?

[bicknellr]

I don't think this is a bug in the polyfill or something that it should attempt to work around. IMHO, LastPass should fix their extension to get the function from the right place and put their replacement in that same place (Document.prototype).

[snuggs]

It's both @joeldenning .The Document.prototype is the appropriate place to do this. Regardless if the alternative is commonplace. Also there is the notion of Document potentially being multiple. From DocumentFragment to <iframe> to HTML Imports, (Even HTML module imports) best to use the Web API Document for enhancements instead of reaching into window.document for monkey patching. Which has been a smelly side effect (pun intended) since Javascript's inception. Also not safe to assume document is what you expect it to be moving forward now that we have a Global Environment Record that is separate from window however has same global variable access as window. This is where const let class memory space are held.

I feel this is outside of the scope of webcomponents/custom-elements. I attempted to go check out LastPass' github and didn't see a project for the plugin. Unfortunate. @bicknellr knows better than me.

[bicknellr]

I had to install the extension and dig around in it to figure out where they did their patch. AFAIK, there's no real source available. :/

[TimvdLippe]

Closing this as a wont-fix. The polyfill is intended to implement the steps as stated in the specification. If users overwrite functions like these, not only this polyfill breaks but also other scripts can break.

[usergenic]

This is my relatively simple workaround/fix https://gist.github.com/usergenic/9baf88a24dcbc77bc808339755a7d436