What causes "task "${name}" was not defined" in vitest-dev/vitest?

Call `.get()` only with names that were registered: the string passed to `bench(name, ...)` or `bench.from(name, ...)`.

vitest-dev/vitest · error · Error

task " " was not defined

Error message

task "${name}" was not defined

What it means

`bench.compare(...)` returns a `BenchStorage<T>` whose `.get(name)` looks up results by registration name. This error fires when `get` is called with a name that matches neither a stored baseline (from `bench.from`) nor a freshly-run result. Names are the literal string passed to `bench(name, ...)` or `bench.from(name, ...)` (or the function's `.name`).

Solutions

Call `.get()` only with names that were registered: the string passed to `bench(name, ...)` or `bench.from(name, ...)`.
Use the typed `BenchStorage<T>` — TypeScript will restrict `.get()` to the union of registered names derived from the `bench.compare(...)` arguments.
Avoid anonymous functions as benchmark names; when passing a function, ensure it has a stable `.name` (no minification stripping).

Example fix

// before
const a = bench('sort', fn)
const storage = await bench.compare(a, b)
storage.get('sorted') // typo

// after
storage.get('sort')

Defensive patterns

Strategy: validation

Validate before calling

const valid = new Set([...registrations].map(r => r.name)); if (!valid.has(requestedName)) throw new Error(`'${requestedName}' not registered; valid: ${[...valid].join(', ')}`)

Type guard

function isKnownName<T extends string>(name: string, set: Set<T>): name is T { return set.has(name as T) }

Try / catch

try { storage.get(name) } catch (e) { if (/was not defined/.test(e.message)) { console.warn('available:', availableNames); return } throw e }

Prevention

Derive lookup names from the registration's `.name` field, not a hand-typed string.
Let TypeScript's `BenchStorage<T>` union narrow the `.get()` argument.
Avoid anonymous functions as benchmark names to keep `.name` stable.

When it happens

Trigger: Calling `storage.get('wrong-name')` after `const storage = await bench.compare(regA, regB)` where `regA.name === 'a'` and `regB.name === 'b'`. The lookup at benchmark.ts:272-276 checks `fromResults?.get(name)` then `results.get(name)` and throws if both miss.

Common situations: Renaming a benchmark but forgetting to update the `.get(name)` consumer; using the function reference's `.name` which is minified/empty in a bundled context; passing the registration object instead of its `.name` string to `.get()`.

Related errors

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/e78d4340863a7804. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/runtime/benchmark.ts:274

    period: data.period,
    totalTime: data.totalTime,
    rank: 0,
    fromStore: true,
  })

  const createCompareStorage = <T extends string>(
    results: Map<string, BenchResult>,
    fromResults?: Map<string, BaselineData>,
  ): BenchStorage<T> => {
    return {
      get(name: T) {
        const stored = fromResults?.get(name)
        if (stored) {
          return stored as BenchResult
        }
        const result = results.get(name)
        if (!result) {
          throw new Error(`task "${name}" was not defined`)
        }
        return result
      },
    }
  }

  interface TaskMeta { perProject?: true }

  const serializeBenchmark = (
    results: BenchResult[],
    name: string,
    taskMeta?: Map<string, TaskMeta>,
    fromTasks?: TestBenchmarkTask[],
  ): TestBenchmark => {
    const tasks: TestBenchmarkTask[] = results.map(result => ({
      name: result.name,
      latency: result.latency,
      throughput: result.throughput,

View on GitHub (pinned to 1fa9837ec2)