vitest-dev/vitest · error · TypeError

any() expects to be passed a constructor function. Please…

Error message

any() expects to be passed a constructor function. Please pass one or use anything() to match any object.

What it means

The Any matcher (expect.any) throws a TypeError when constructed with undefined. It expects a constructor function/class so it can compare instances; if you genuinely want to match anything (object, primitive, anything), use expect.anything() instead.

Solutions

1. Use expect.anything() if you want to match any non-null/non-undefined value.
2. Fix the import so the constructor/class is actually defined (check the export and the import path).
3. Add a runtime assert that the symbol is defined before passing it to expect.any.

Example fix

// before
expect(mock).toHaveBeenCalledWith(expect.any(undefined))
// after
expect(mock).toHaveBeenCalledWith(expect.anything())
// or, if you have a real class:
expect(mock).toHaveBeenCalledWith(expect.any(User))

function asAnyOrAnything(sample) {
  if (sample === undefined) return expect.anything()
  if (typeof sample !== 'function') {
    throw new TypeError('expect.any needs a constructor function')
  }
  return expect.any(sample)
}

function isConstructor(v): v is new (...args: unknown[]) => unknown {
  return typeof v === 'function'
}

When it happens

Trigger: expect.any(sample) where sample is undefined — typically an undefined class due to a missing/bad import, a circular import that returned undefined, or a conditional that produced undefined.

Common situations: Importing a class that does not exist or is not exported from the target module; type-only import that got stripped; referencing a global that is undefined in the current environment.

Related errors

• Expected is not a Number
• Expected is not a string
• Expected is not a String or a RegExp
• Precision is not a Number
• You must provide an array to

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/0f9cab7169a0382d. Report an issue: GitHub.

Appendix: source

Thrown at packages/expect/src/jest-asymmetric-matchers.ts:231

            ),
          ))

    return this.inverse ? !result : result
  }

  toString() {
    return `Array${this.inverse ? 'Not' : ''}Containing`
  }

  getExpectedType() {
    return 'array'
  }
}

export class Any extends AsymmetricMatcher<any> {
  constructor(sample: unknown) {
    if (typeof sample === 'undefined') {
      throw new TypeError(
        'any() expects to be passed a constructor function. '
        + 'Please pass one or use anything() to match any object.',
      )
    }
    super(sample)
  }

  fnNameFor(func: Function): string {
    if (func.name) {
      return func.name
    }

    const functionToString = Function.prototype.toString

    const matches = functionToString
      .call(func)
      .match(/^(?:async)?\s*function\s*(?:\*\s*)?([\w$]+)\s*\(/)
    return matches ? matches[1] : '<anonymous>'

View on GitHub (pinned to 1fa9837ec2)