read-file-with-err-return.ts

const readFile = async (file: string): Promise<[Error | null, string]> => {
  try {
    const text = await Deno.readTextFile(file);
    return [null, text];
  } catch (err) {
    return [err, ""];
  }
};

const main = async () => {
  const file = Deno.env.get("FILE");
  if (!file) {
    console.log("file name required.");
    return;
  }

  console.log(`reading ${file} ...`);

  const [err, text] = await readFile(file);
  if (err != null) {
    console.error(`failed to read ${file}: ${err}`);
    return;
  }

  console.log(`file content:\n${text}`);
};

main();