The loadingdone event fires when the document has loaded all fonts.

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener("loadingdone", (event) => {});

onloadingdone = (event) => {};

In the following example, when the font Ephesis has finished loading, "Font loading complete" is printed to the console.

document.fonts.onloadingdone = () => {
  console.log("Font loading complete");
};

(async () => {
  await document.fonts.load("16px Ephesis");
})();