read-file-generic-trycatch.ts

type PromiseFunc = (...args: any[]) => Promise<any>;

type TryCatch<Func extends PromiseFunc> = (
  ...args: [...Parameters<Func>]
) => Promise<[Error | null, Awaited<ReturnType<Func>> | null]>;

const trycatch =
  <Func extends PromiseFunc>(f: Func): TryCatch<Func> => async (...args) => {
    try {
      const v = await f(...args);
      return [null, v]
    } catch (err) {
      return [err as Error, null];
    }
  };

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 trycatch(Deno.readTextFile)(file);
  if (err !== null) {
    console.error(`failed to read ${file}: ${err}`);
    return;
  }

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

main();