denoland/deno · error · TypeError

Cannot create cron job, a single handler is required: two ha

Error message

Cannot create cron job, a single handler is required: two handlers were specified

What it means

Deno.cron accepts either (name, schedule, handler) or (name, schedule, options, handler). When the third argument is a function, the fourth argument must be absent; supplying both counts as two handlers and throws.

Source

Thrown at ext/cron/01_cron.ts:137

    );
  }
  if (schedule === undefined) {
    throw new TypeError(
      "Cannot create cron job, a schedule is required: received 'undefined'",
    );
  }

  schedule = parseScheduleToString(schedule);

  let handler: () => Promise<void> | void;
  let options:
    | { backoffSchedule?: number[]; signal?: AbortSignal }
    | undefined = undefined;

  if (typeof handlerOrOptions1 === "function") {
    handler = handlerOrOptions1;
    if (handler2 !== undefined) {
      throw new TypeError(
        "Cannot create cron job, a single handler is required: two handlers were specified",
      );
    }
  } else if (typeof handler2 === "function") {
    handler = handler2;
    options = handlerOrOptions1;
  } else {
    throw new TypeError("Cannot create cron job: a handler is required");
  }

  const rid = op_cron_create(
    name,
    schedule,
    options?.backoffSchedule,
  );

  if (options?.signal) {
    const signal = options?.signal;

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Delete the extra handler argument.
2. If options (backoffSchedule, signal) are needed, make the third argument the options object and the fourth the single handler.

Example fix

// before
Deno.cron('n', '* * * * *', runA, runB);
// after
Deno.cron('n', '* * * * *', runA);

if (typeof handlerOrOptions1 === 'function' && handler2 !== undefined) {
  throw new Error('pass exactly one handler');
}
Deno.cron(name, schedule, handlerOrOptions1, handler2);

When it happens

Trigger: Deno.cron('n', '* * * * *', fn, fn2) — any fourth argument alongside a function third argument.

Common situations: Copy-paste from an older or imagined API with a completion callback; merging two code paths that each supplied a handler.

Related errors

• Invalid cron schedule: start=${start}, end=${end}, every=${e
• Cannot create cron job, a unique name is required: received
• Cannot create cron job, a schedule is required: received 'un
• Cannot create cron job: a handler is required
• Delay must be >= 0: received ${delay}

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/0b41650cea49b525. Report an issue: GitHub.