jestjs/jest · error · Error

Cannot replace the `${String(propertyKey)}` property because

Error message

Cannot replace the `${String(propertyKey)}` property because it has a getter. Use `jest.spyOn(object, '${String(propertyKey)}', 'get').mockReturnValue(value)` instead.

What it means

Thrown by jest.replaceProperty when the descriptor has a getter. Replacing a getter-backed value would silently discard the getter semantics, so Jest refuses and points you to spyOn with accessType 'get', which correctly wraps the getter.

Source

Thrown at packages/jest-mock/src/index.ts:1490

    while (!descriptor && proto !== null) {
      descriptor = Object.getOwnPropertyDescriptor(proto, propertyKey);
      proto = Object.getPrototypeOf(proto);
    }
    if (!descriptor) {
      throw new Error(
        `Property \`${String(
          propertyKey,
        )}\` does not exist in the provided object`,
      );
    }
    if (!descriptor.configurable) {
      throw new Error(
        `Property \`${String(propertyKey)}\` is not declared configurable`,
      );
    }

    if (descriptor.get !== undefined) {
      throw new Error(
        `Cannot replace the \`${String(
          propertyKey,
        )}\` property because it has a getter. Use \`jest.spyOn(object, '${String(
          propertyKey,
        )}', 'get').mockReturnValue(value)\` instead.`,
      );
    }

    if (descriptor.set !== undefined) {
      throw new Error(
        `Cannot replace the \`${String(
          propertyKey,
        )}\` property because it has a setter. Use \`jest.spyOn(object, '${String(
          propertyKey,
        )}', 'set').mockReturnValue(value)\` instead.`,
      );
    }

View on GitHub (pinned to 8e6d128e4a)

Solutions

Use jest.spyOn(obj,'x','get').mockReturnValue(value) to override the getter's return.
If you need to fully swap the property, redefine it without a getter first (only if configurable).
Prefer module-level jest.mock for source-owned code.

Example fix

// before
jest.replaceProperty(obj, 'version', '2.0'); // version has a getter
// after
jest.spyOn(obj, 'version', 'get').mockReturnValue('2.0');

Defensive patterns

Strategy: validation

Validate before calling

const d = Object.getOwnPropertyDescriptor(obj, propertyKey);
if (d?.get) {
  jest.spyOn(obj, propertyKey, 'get').mockReturnValue(value);
} else {
  jest.replaceProperty(obj, propertyKey, value);
}

Type guard

const hasGetter = (o: object, k: PropertyKey): boolean =>
  Object.getOwnPropertyDescriptor(o, k)?.get !== undefined;

Prevention

Check the descriptor's get/set before choosing replaceProperty.
Use spyOn(obj, prop, 'get') for getter-backed values.
Centralise property-mocking decisions in a helper.

When it happens

Trigger: jest.replaceProperty(obj,'x',v) where x is declared with Object.defineProperty({get:...}) or a class accessor property.

Common situations: Class getter properties; config objects with computed getters; framework objects exposing derived values.

Related errors

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/0ee21c232fea4465. Report an issue: GitHub.