4. Throw errors JavaScript can handle

trip.lucent.ts

src/trip.lucent.ts

import { error } from "lucent:core";

export type Fix = { latitude: number; longitude: number; time: number };

const EARTH_RADIUS_M = 6371000;
…
  private fixes: Fix[] = [];

  add(fix: Fix): void {
    const last = this.fixes[this.fixes.length - 1];
    if (last && fix.time < last.time) {
      throw error(
        "E_OUT_OF_ORDER",
        `A fix at ${fix.time} ms comes before the last one, at ${last.time} ms`,
      );
    }
    this.fixes.push(fix);
  }

…
  }

  summary(): TripSummary {
    if (this.fixes.length < 2) throw error("E_TOO_SHORT", "A trip needs at least two fixes");
    let meters = 0;
    let topSpeed = 0;
    for (let i = 1; i < this.fixes.length; i++) {

App.tsx

App.tsx

const trip = new Trip();
for (const fix of walk) trip.add(fix);

/** Adds a fix, skipping one that arrives late instead of failing the whole trip. */
function record(fix: (typeof walk)[number]): void {
  try {
    trip.add(fix);
  } catch (e) {
    if ((e as { code?: string }).code !== "E_OUT_OF_ORDER") throw e;
    console.warn((e as Error).message);
  }
}

record({ latitude: 48.86, longitude: 2.33, time: 5 * 60 * 1000 }); // late: skipped

export default function App() {
  const [shape, setShape] = useState<number | null>(null);

error(code, message) from lucent:core makes an Error with a code. JavaScript receives an ordinary Error, with the same message and code, and a stack whose first frame is the line in trip.lucent.ts that threw.

Test the code, not the message: codes are for code, messages are for people. Here, a fix that arrives late is skipped, and any other error still reaches React.

Run it

The screen is unchanged. Metro's output shows the warning for the late fix: A fix at 300000 ms comes before the last one, at 2400000 ms.