You may want to look into the Web Bluetooth and Web Bluetooth Scanning specs:
https://webbluetoothcg.github.io/web-bluetooth/
https://webbluetoothcg.github.io/web-bluetooth/scanning.html
“Scanning” is in general more useful in the context of beacons, but it’s still in the very early stages and it’s not implemented in any web browser.
The “regular” Web Bluetooth is already widely implemented though:
https://github.com/WebBluetoothCG/web-bluetooth/blob/master/implementation-status.md