How do I create a webp image file using pure client side javascript without the canvas?

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Javascript

BH
Title says it all.

I'm trying to do image processing inside a web worker (ultimately hoping to try to do WebM encoding directly), I currently have an array of RGBA raw data and can convert it into various other formats, but in order to make it easier to encode it directly into a WebM file I want to make a webp image format
Everywhere I look directs to the webpjs library, but the main website that supposedly explains it is offline

I was able to find what seems like a copy of it https://github.com/obartra/webpjs but there's no documentation, and after I tried including the script file and analyzing the functions I was not able to figure anything out, at the minified code is very cryptic.

Someone recently showed me what seems to be the updated website http://libwebpjs.hohenlimburg.org/ but many of the links are broken and even with wayback it's hard to find what source file is used in the example on the homepage? It's also not clear if webpjs is the same as libwebpjs

Any ideas?

What I have tried:

BH

See above.

I've tried searching other places and asking other people in other places.