TIL about window.stop() - the key to this entire thing working, it's causes the browser to stop loading any more assets: https://developer.mozilla.org/en-US/docs/Web/API/Window/stop

Apparently every important browser has supported it for well over a decade: https://caniuse.com/mdn-api_window_stop

Here's a screenshot illustrating how window.stop() is used - https://gist.github.com/simonw/7bf5912f3520a1a9ad294cd747b85... - everything after <!-- GWTAR END is tar compressed data.

Posted some more notes on my blog: https://simonwillison.net/2026/Feb/15/gwtar/

Not the inverse, but for any SPA (not framework or library) developers seeing this, it's probably worth noting that this is not better than using document.write, window.open and simular APIs.

But could be very interesting for use cases where the main logic lives on the server and people try to manually implement some download- and/or lazy-loading logic.

Still probably bad unless you're explicitly working on init and redirect scripts.

Neat! I didn't know about this either.

Php has a similar feature called __halt_compiler() which I've used for a similar purpose. Or sometimes just to put documentation at the end of a file without needing a comment block.