my use case: Testing a third party widget on a website.
For that, we load the widget on the third party as a <script src='https://cdn.com/widget.js'/> tag. What I'd like to do is intercept that JS request and replace https://cdn.com/widget.js with https://localhost:3000/dist/widget.js.
This is so that we can run the cypress tests with the local version of the widget (run in CI on a PR), and make sure that the PR doesn't break the e2e tests, before merging it.
You can modify the body of the initial visit using cy.intercept()
cy.intercept(url, (req) => {
req.continue((res) => {
res.body = res.body.replace('https://cdn.com/widget.js', 'https://localhost:3000/dist/widget.js')
})
}).as('page')
cy.visit(url)
cy.wait('@page')
.its('response.body')
.should('contain', "<script src='https://localhost:3000/dist/widget.js'/>")
You can use blockHosts to prevent the script at that domain from loading completely. That won't let you replace it with a fake wdiget though.
In order to replace the response with something else, you could use Intercept instead.
There's an interesting example of using this and stub to replace Google Analytics here - https://github.com/cypress-io/cypress-example-recipes/tree/master/examples/stubbing-spying__google-analytics