The loadingerror event fires when fonts have finished loading, but some or all fonts have failed to load.

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

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

onloadingerror = (event) => {};

In the following example, if the font Ephesis fails to load, "Font loading error" is printed to the console.

document.fonts.onloadingerror = () => {
  console.log("Font loading error");
};

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