jestjs/jest · 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

expect.any(constructor) builds an asymmetric matcher that matches values `instanceof` the given constructor (or by typeof for the built-in wrappers like String, Number). The Any constructor throws a TypeError when sample is undefined — i.e. when expect.any() is called with no argument — because there is no constructor to match against. The message suggests expect.anything() for the common case of wanting to match any non-null/undefined value.

Solutions

1. If you want to match any non-null/undefined value, use `expect.anything()` instead of `expect.any()`.
2. If you want to match a specific type, pass the constructor: `expect.any(String)`, `expect.any(MyClass)`.
3. Check that the constructor reference you passed is actually defined (e.g. the import resolved).

Example fix

// before
expect(user).toEqual({ id: expect.any(), name: expect.any(String) }); // expect.any() throws

// after
expect(user).toEqual({ id: expect.any(Number), name: expect.any(String) });
// or, to allow any non-null value:
expect(user).toEqual({ id: expect.anything(), name: expect.anything() });

// Ensure a constructor is present before building an Any matcher.
function anyOf(ctor) {
  if (ctor === undefined) {
    throw new TypeError('Pass a constructor to expect.any, or use expect.anything()');
  }
  return expect.any(ctor);
}

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

const matcher = isConstructor(Ctor) ? expect.any(Ctor) : expect.anything();

When it happens

Trigger: Writing `expect.any()` with zero arguments, or passing a variable that evaluates to undefined where a constructor was intended. The guard fires only for the literal undefined case (not null or other falsy values, which become matchers that match via instanceof).

Common situations: Typo intending expect.anything(); passing an imported symbol that failed to import (undefined); dynamically selecting a constructor from a map lookup that misses; copy-pasting a matcher template and forgetting to fill in the constructor.

Related errors

• Expected is not a string
• Expected is not a String or a RegExp
• You must provide an array to
• You must provide an object to
• expect.customEqualityTesters: Must be set to an array of…

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/14d0cd5ffdac8b7a. Report an issue: GitHub.

Appendix: source

Thrown at packages/expect/src/asymmetricMatchers.ts:90

      // eslint-disable-next-line @typescript-eslint/no-empty-function
      dontThrow: () => {},
      ...getState<MatcherState>(),
      equals,
      isNot: this.inverse,
      utils,
    };
  }

  abstract asymmetricMatch(other: unknown): boolean;
  abstract toString(): string;
  getExpectedType?(): string;
  toAsymmetricMatcher?(): string;
}

class Any extends AsymmetricMatcher<any> {
  constructor(sample: unknown) {
    if (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);
  }

  asymmetricMatch(other: unknown) {
    if (this.sample === String) {
      // eslint-disable-next-line unicorn/no-instanceof-builtins
      return typeof other === 'string' || other instanceof String;
    }

    if (this.sample === Number) {
      // eslint-disable-next-line unicorn/no-instanceof-builtins
      return typeof other === 'number' || other instanceof Number;
    }

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