How do we modify Request or Response Dynamically

Q: How do we modify Request or Response Dynamically

Cypress intercepts a POST request to /api/login. It doesn’t block the request immediately — instead, it uses a callback to manipulate the response. In this case, it fakes the login token in the reply. cy.intercept('POST', '/api/login', (req) => { req.reply((res) => { res.send({ token: 'fake-token-123' }); }); }).as('fakeLogin');

Difficulty: 5/10

cy.intercept, request/response stubbing, dynamic modification

cy.intercept() lets you:

1
Cypress intercepts a POST request to /api/login.
2
It doesn’t block the request immediately — instead, it uses a callback to manipulate the response.
3
In this case, it fakes the login token in the reply.

You want to customize responses on the fly, or perhaps simulate a successful login without hitting a real auth server.

Scenario Questions

0-2 years experience

1We have a login page that sends a POST to /api/auth. How would you use Cypress to change the username field in the request before it reaches the server?
2During a test you need the API to return a 200 with a custom JSON payload instead of the real data. Walk me through the code you’d write to achieve that.

2-5 years experience

1Our test suite intermittently fails because a third‑party service sometimes returns extra fields. How would you intercept the response and strip those fields dynamically?

Follow-up Questions

What edge cases can cause a modified response to break downstream UI logic?
How would you debug a test that suddenly stops intercepting a request?
When would you prefer a fixture over programmatic mutation?

How do we modify Request or Response Dynamically

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Scenario Questions

Follow-up Questions