A friend of mine is currently attempting to create a VR museum using models he's created himself as well as some open-source ones pulled from Sketchfab online. He needs these files to be .glbs, but Sketchfab only allows downloading the models in glTF and USBZ format.

There are ways to convert from glTF to GLB, but they're tedious and he currently has to convert them one at a time, which is inconvenient for any meaningful number of files. Automating it on-device doesn't make sense, because he normally downloads files in small batches when a new subject catches his focus, and running a script after each time would be just as inconvenient.

I'm looking to create a Chrome browser extension that would allow him to directly download these files as GLBs, no conversion necessary, which is the solution that works best with his workflow.

To do this, I need my browser extension to pull the glTF data from Sketchfab's download button, run the transformation process, and then save the modified file to his computer. This seems like it should be possible, but I have no idea how to even get started with the first bit.

I've tried to use developer tools to find the download link attached to the button so that I could issue a GET request to that, then process the resulting data and use Chrome's download API to do the rest. The only issue is, the download link doesn't appear to be anywhere on the page. I've taken a heap snapshot, then monitored the network when I clicked the download button, and the link my browser sends the GET request to is nowhere to be found in the heap before the button is clicked. I'm guessing it's constructed via JavaScript on the fly, but I have no clue how I'd go about predicting the link for myself.

If anyone has any guidance for how I can grab this data from a browser extension, it'd be much appreciated. I know it must be possible - if you can get the data by clicking the download button, you should be able to get it programmatically too. How precisely to do that, though, is something I can't seem to figure out.

TLDR: I'm trying to build an extension that allows conversion of file format from glTF to GLB prior to download, but am running into trouble getting access to the data I need to convert. Any advice?