vitest-dev/vitest · error · TypeError

`bench()` does not accept options as the third argument. Pas

Error message

`bench()` does not accept options as the third argument. Pass options as the second argument instead: `bench(name, options, fn)`.

What it means

The `bench()` overloads are `bench(name, fn)` and `bench(name, options, fn)` — options come SECOND. `normalizeBenchArgs` (see `benchmark.ts:574`) treats a function second argument as `fn`; if a third argument is also present, it assumes you tried `bench(name, fn, options)` (options last) and throws this `TypeError` to redirect you to the correct order.

Source

Thrown at packages/vitest/src/runtime/benchmark.ts:574

  }

  return bench
}

function formatModuleId(moduleId: string, root: string): string {
  if (!root || !isAbsolute(moduleId)) {
    return moduleId
  }
  return relative(root, moduleId)
}

function normalizeBenchArgs(
  a: BenchFn | BenchFnOptions,
  b: BenchFn | BenchFnOptions | undefined,
): { fn: BenchFn; fnOpts: BenchOptions | undefined; writeResult: string | undefined; perProject: boolean } {
  if (typeof a === 'function') {
    if (b !== undefined) {
      throw new TypeError('`bench()` does not accept options as the third argument. Pass options as the second argument instead: `bench(name, options, fn)`.')
    }
    return { fn: a, fnOpts: undefined, writeResult: undefined, perProject: false }
  }
  if (typeof b !== 'function') {
    throw new TypeError('`bench()` expects a benchmark function. Call `bench(name, fn)` or `bench(name, options, fn)`.')
  }
  // Strip vitest-specific fields only when present so we don't allocate a new
  // object — preserving referential identity matters: users inspect
  // `registration.fnOpts` and the provider sees the same object the caller
  // passed in.
  if (a.writeResult === undefined && a.perProject === undefined) {
    return { fn: b, fnOpts: a as BenchOptions, writeResult: undefined, perProject: false }
  }
  const { writeResult, perProject, ...fnOpts } = a
  return {
    fn: b,
    fnOpts: Object.keys(fnOpts).length > 0 ? fnOpts as BenchOptions : undefined,
    writeResult,

View on GitHub (pinned to d568f8ce37)

Solutions

Move options to the second slot: `bench('sort', { iterations: 100 }, () => x())`.
If you don't need options, drop the third argument: `bench('sort', () => x())`.

Example fix

// before
bench('sort', () => sortArr(), { iterations: 100 })

// after
bench('sort', { iterations: 100 }, () => sortArr())

Defensive patterns

Strategy: validation

Validate before calling

// Enforce the correct argument order before calling bench.
function benchSafe(name: string, fnOrOpts: any, maybeOpts?: any) {
  if (typeof fnOrOpts === 'function' && maybeOpts !== undefined) {
    // user did bench(name, fn, opts) — reorder
    return bench(name, maybeOpts, fnOrOpts)
  }
  return bench(name, fnOrOpts, maybeOpts)
}

Try / catch

try {
  bench(name, fn, opts)
} catch (e) {
  if (e instanceof TypeError && /does not accept options as the third argument/.test(e.message)) {
    bench(name, opts, fn) // correct order
  } else throw e
}

Prevention

Remember the signature: bench(name, options?, fn) — options come BEFORE fn.
Drop the options object entirely when you don't need it.
Use an editor snippet that emits the correct argument order.

When it happens

Trigger: Calling `bench('sort', () => x(), { iterations: 100 })` — fn in slot 2, options in slot 3.

Common situations: Migrating from another benchmark API (tinybench, jest) where options come last; muscle memory from `it(name, fn, timeout)`.

Related errors

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/bac948dff8b41bf2.json. Report an issue: GitHub.