Throw and handle errors

module

config.lucent.ts

import { error, errorCode } from "lucent:core";

export type Config = { name: string; retries: number };

export function parseConfig(text: string): Config {
  if (text.trim().length === 0) throw error("E_EMPTY", "The config is empty");
  return JSON.parse(text) as Config;
}

export function retriesOr(text: string, fallback: number): number {
  try {
    return parseConfig(text).retries;
  } catch (e) {
    if (e instanceof Error && errorCode(e) === "E_EMPTY") return fallback;
    throw e;
  }
}

JS usage

App.tsx

try {
  parseConfig("");
} catch (e) {
  if ((e as { code?: string }).code === "E_EMPTY") showDefaults();
  else throw e;
}

• error(code, message) from lucent:core makes an Error with a code. Test the code, not the message.
• JavaScript receives an Error, TypeError or RangeError, with the same name, message and code. Its stack starts at the line that made the error.
• Only Error values can be thrown (LUCENT1006). Subclasses reach JavaScript as plain errors, with their name, message and code.
• An async export's error rejects its promise. A JS callback's error, or a rejected promise you await, is thrown in Lucent, with its code.
• SDK errors arrive the same way: a Java exception's code is its class, and an NSError's is domain:code.

An error that nothing catches in an SDK callback is logged: [lucent] uncaught exception in …, in the unified log on iOS and logcat on Android.