Olorin Auto-Printer by Kyle Hall

1. The web application embeds a print button — in Koha, notice/slip
   templates carry it:

html
<button id="webPrint" data-printer="receipt_printer" data-print="#receipt">Print</button>

data-printer names one of five logical printers — receipt_printer,
sticker_printer, paper_printer, full_sheet_printer,
label_printer — and data-print is a CSS selector for the element whose
contents should print. Any element with the olorinPlugin class works the
same way.

1. Wrap the printable part of the slip:

html
<span id="receipt"> ... slip content ... </span>

1. To print automatically when the page loads, trigger a click on the
   button from the page's own JavaScript. In Koha that means setting the
   IntranetSlipPrinterJS system preference to:

javascript
setTimeout(function () {
$("#webPrint").trigger("click");
}, 1000);

(Any page script that dispatches a real click works — jQuery is not
required.)

1. The extension's options page maps each logical printer to a real OS
   printer, with per-printer page size, margins, orientation, number of
   copies, and duplex (long edge / short edge) mode. Settings are stored by
   the companion app, so they are shared by every browser on the machine.

Pages can react to print outcomes by listening for a DOM event:

document.addEventListener("olorin:print-result", (e) => console.log(e.detail));
// e.detail = { success: true } or { success: false, error: "..." }