UEFI Bindings for JavaScript
Promethee loads script.js from the boot volume and runs it. That script is your bootloader. If you can do it with UEFI services, you can do it in JavaScript.
Fetch dependencies: ./get-deps
Build and run in QEMU: make run
Your entrypoint is script.js. The run target copies it to the UEFI FAT volume as \script.js.
In script.js:
var gop = efi.SystemTable.BootServices.LocateProtocol(efi.guid.GraphicsOutput);
if (gop) {
var red = { r: 255, g: 0, b: 0 };
gop.Blt(red, 'EfiBltVideoFill', 0, 0, 50, 50, 200, 120, 0);
}