How do I mock the window.fb object in a Chrome tab using Playwright?


Mocking window.fb with Playwright

Yes, you can mock window.fb when opening a Chrome tab with Playwright. You can use the page.addInitScript() method to set up mocks before the page starts loading. This lets you modify browser APIs and test your application's response.

Here's how you can do it:

await page.addInitScript(() => {
  const mockFb = {
    property1: 'mocked value',
    method1: () => { /* mocked implementation */ },

  Object.defineProperty(window, 'fb', { value: mockFb });

In this code, mockFb is an object with mocked properties and methods for window.fb. You can customize these according to your testing needs. Object.defineProperty() is used to override the existing window.fb with our mock object. This ensures that any references to window.fb in your application will now point to our mocked version.

Remember, this approach only works within Playwright's context during automated tests. If you want to modify the actual behavior of browser APIs in a live Chrome tab or console session outside of Playwright, you would need to edit the window object directly in those environments.

In short, Playwright's page.addInitScript() method lets you easily mock browser APIs like window.fb. This allows you to test your application's behavior with customized API responses without the need to edit the window object manually.


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Rayrun is a community for QA engineers. I am constantly looking for new ways to add value to people learning Playwright and other browser automation frameworks. If you have feedback, email luc@ray.run.