In one project, I am using a worker to perform some heavy tasks. When trying to commit changes, jest gives a ReferenceError. I had to use the code below to create a reference for Worker to run on jest.

window.Worker = jest.fn().mockImplementation(() => ({
  postMessage: jest.fn(),
  onmessage: jest.fn(),
  onerror: jest.fn(),
  terminate: jest.fn(),
}));

Here is more info about the function itself.

Here is another solution.

a. First, I created a dummy worker.

class Worker {
  constructor() {
    this.onmessage = () => {};
  }

  postMessage(msg) {
    this.onmessage(msg);
  }
  terminate() { // I am actually calling this method, so I had to add it here too.
    () => {};
  }
}

export default Worker;

b. Then I placed this code in __mocks__ directory

c. Imported and assigned to the window object:

import Worker from '../../__mocks__/worker';
window.Worker = Worker;

On github was issue open [here](https://github.com/jestjs/jest/issues/3449#issuecomment-750345973).

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