denoland/deno · error · Error

'options' requires at least one option to be true

Error message

'options' requires at least one option to be true

What it means

checkOpenOptions validates the options bag passed to Deno.open/openSync before anything is opened. At least one flag (read, write, append, truncate, create, createNew) must be true, otherwise the operation would have no effect at all, so a plain Error is thrown. An empty object {} also fails this check since zero values are true.

Source

Thrown at ext/fs/30_fs.js:801

  }

  async unlock() {
    await op_fs_funlock_async(this.#rid);
  }

  [SymbolDispose]() {
    core.tryClose(this.#rid);
  }
}

function checkOpenOptions(options) {
  if (
    ArrayPrototypeFilter(
      ObjectValues(options),
      (val) => val === true,
    ).length === 0
  ) {
    throw new Error(
      "'options' requires at least one option to be true",
    );
  }

  if (options.truncate && !options.write) {
    throw new Error(
      "'truncate' option requires 'write' to be true",
    );
  }

  const createOrCreateNewWithoutWriteOrAppend =
    (options.create || options.createNew) &&
    !(options.write || options.append);

  if (createOrCreateNewWithoutWriteOrAppend) {
    throw new Error(
      "'create' or 'createNew' options require 'write' or 'append' to be true",
    );

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Pass at least one true flag, e.g. { read: true }
2. Map Node flags: 'r' -> { read: true }, 'w' -> { write: true, create: true, truncate: true }, 'a' -> { append: true, create: true }
3. Validate programmatically-built options before calling open

Example fix

// before
await Deno.open("/tmp/x", {}); // Error

// after
await Deno.open("/tmp/x", { read: true });

function hasAnyTrueFlag(options) {
  return Object.values(options).some((v) => v === true);
}
if (!hasAnyTrueFlag(options)) {
  options = { ...options, read: true }; // or reject with a clear message
}
await Deno.open(path, options);

function isOpenOptionsValid(options: Record<string, unknown>): boolean {
  return Object.values(options).some((v) => v === true);
}

try {
  file = await Deno.open(path, options);
} catch (err) {
  if (err instanceof Error && err.message === "'options' requires at least one option to be true") {
    file = await Deno.open(path, { ...options, read: true });
  } else throw err;
}

When it happens

Trigger: Deno.open(path, {}) or Deno.openSync(path, { read: false, write: false }) — an options object in which no value equals true.

Common situations: Options built programmatically where all flags end up false depending on input; porting Node's fs.open flag strings and passing an empty object for 'r'; a falsy flag typo like read: flase (misspelling) silently evaluating to undefined.

Related errors

• 'truncate' option requires 'write' to be true
• 'create' or 'createNew' options require 'write' or 'append'
• A file exists at the destination: ${destStr}
• ERR_MISSING_ARGS
• No callback function supplied

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/8b7fe20b8064069c. Report an issue: GitHub.