intercept

Spy and stub network requests and responses.

Syntax

// spying only
cy.intercept(url)
cy.intercept(method, url)
cy.intercept(routeMatcher)

See arguments url, method and routeMatcher

// spying and response stubbing
cy.intercept(url, staticResponse)
cy.intercept(method, url, staticResponse)
cy.intercept(routeMatcher, staticResponse)
cy.intercept(url, routeMatcher, staticResponse)

See staticResponse argument

// spying, dynamic stubbing, request modification, etc.
cy.intercept(url, routeHandler)
cy.intercept(method, url, routeHandler)
cy.intercept(routeMatcher, routeHandler)
cy.intercept(url, routeMatcher, routeHandler)

See routeHandler argument

Usage

Correct Usage

// spying
cy.intercept('/users/**')
cy.intercept('GET', '/users*')
cy.intercept({
  method: 'GET',
  url: '/users*',
  hostname: 'localhost',
})

// spying and response stubbing
cy.intercept('POST', '/users*', {
  statusCode: 201,
  body: {
    name: 'Peter Pan',
  },
})

// spying, dynamic stubbing, request modification, etc.
cy.intercept('/users*', { hostname: 'localhost' }, (req) => {
  /* do something with request and/or response */
})

Arguments

method (String)

Match the route to a specific HTTP method (GET, POST, PUT, etc).

url (String, Glob, RegExp)

Specify the URL to match. See Matching url for examples.

Alternatively, specify the URL via the routeMatcher argument (below).

routeMatcher (RouteMatcher)

routeMatcher is an object used to match the incoming HTTP requests with this intercepted route.

All properties are optional but all those that are set must match for the request to be intercepted. If a string is passed to any property, it will be glob-matched against the request using Cypress.minimatch.

OptionDescription
authHTTP Basic Authentication (object with keys username and password)
headersHTTP request headers (object)
hostnameHTTP request hostname
httpstrue: only secure (https://) requests, false: only insecure (http://) requests
methodHTTP request method (matches any method by default)
middlewaretrue: match route first and in defined order, false: match route in reverse order (default)
pathHTTP request path after the hostname, including query parameters
pathnameLike path, but without query parameters
portHTTP request port(s) (number or Array)
queryParsed query string (object)
timesMaximum number of times to match (number)
urlFull HTTP request URL

See examples below.

staticResponse (StaticResponse)

By passing in a StaticResponse as the last argument, you can statically define (stub) a response for matched requests including the body of the response, as well as the headers and HTTP status code:

OptionDescription
statusCodeHTTP response status code
headersHTTP response headers
bodyServe a static response body (object, string, ArrayBuffer)
fixtureServe a fixture as the HTTP response body

StaticResponse also provides options for simulating a degraded or broken network connection:

OptionDescription
forceNetworkErrorForce an error by destroying the browser connection
delayMinimum network latency or delay to add to the response time (milliseconds)
throttleKbpsMaximum data transfer rate of the response (kilobits/second)

Note: All properties are optional.

See Stubbing a response with a StaticResponse object for an example.

See also StaticResponse objects.

routeHandler (Function)

The routeHandler function is called whenever a request is matched, with the first argument being the request object. From inside the callback, you have access to the entire request-response where you can modify the outgoing request, send a response, access the real response, and more.

See "Intercepted requests" and Request/Response Modification with routeHandler.

Yields

  • cy.intercept() yields null.
  • cy.intercept() can be aliased, but otherwise cannot be chained further.
  • Waiting on an aliased cy.intercept() route using cy.wait() will yield an object that contains information about the matching request/response cycle. See Using the yielded object for examples of how to use this object.

Examples

Matching url

You can provide the exact URL to match or use pattern-matching to match many URLs at once, either with globs or with regex. See Glob Pattern Matching URLs.

// match any request that exactly matches the URL
cy.intercept('https://prod.cypress.io/users')

// match any request that satisfies a glob pattern
cy.intercept('/users?_limit=*')

// match any request that satisfies a regex pattern
cy.intercept(/\/users\?_limit=(3|5)$/)

Matching method

cy.intercept('/users')
// matches this: GET http://localhost/users
// ...and this, too: POST http://localhost/users

cy.intercept('GET', '/users')
// matches this: GET http://localhost/users
// ...but not this: POST http://localhost/users

Matching with RouteMatcher

Specifying a method and url to match can also be acheived by passing the routeMatcher object into cy.intercept instead:

// These both yield the same result:
cy.intercept({ method: 'GET', url: '**/users' })
cy.intercept('GET', '**/users')
// Match any type of request with the pathname `/search`
// and the query paramater 'q=some+terms'
cy.intercept({
  pathname: '/search',
  query: {
    q: 'some terms',
  },
}).as('searchForTerms')
cy.intercept(
  {
    // this RegExp matches any URL beginning with
    // 'http://api.example.com/' and ending with '/edit' or '/save'
    url: /^http:\/\/api\.example\.com\/.*\/(edit|save)/,
    // matching requests must also contain this header
    headers: {
      'x-requested-with': 'exampleClient',
    },
  }
})
// this example will cause 1 request to `/temporary-error`
// to receive a network error and subsequent requests will
// not match this `RouteMatcher`
cy.intercept('/temporary-error', { times: 1 }, { forceNetworkError: true })

Pattern Matching

// match updates to the `/users` endpoint using glob matching
cy.intercept({
  method: '+(PUT|PATCH)',
  url: '**/users/*',
})
// matches:
//   PUT /users/1
//   PATCH /users/1
//   doesn't match
//   GET /users
//   GET /users/1

// same as above, but using regex
cy.intercept({
  method: '/PUT|PATCH/',
  url: '**/users/*',
})

Aliasing an intercepted route

While cy.intercept doesn't yield anything, you can chain .as to it to create an alias which can be used to wait on a request.

cy.intercept('GET', '/users').as('getAllUsers')
cy.intercept('POST', '/users').as('createUser')

Aliasing individual requests

Aliases can be set on a per-request basis by setting the alias property of the intercepted request. This is especially useful when intercepting GraphQL requests:

cy.intercept('POST', '/graphql', (req) => {
  if (req.body.hasOwnProperty('query') && req.body.query.includes('mutation')) {
    req.alias = 'gqlMutation'
  }
})

// assert that a matching request has been made
cy.wait('@gqlMutation')

Waiting on a request

Use cy.wait() with aliasing an intercepted route to wait for the request/response cycle to complete.

With URL

cy.intercept('http://example.com/settings').as('getSettings')

// once a request to get settings responds, 'cy.wait' will resolve
cy.wait('@getSettings')

With RouteMatcher

cy.intercept({
  url: 'http://example.com/search*',
  query: { q: 'expected terms' },
}).as('search')

// once any type of request to search with a querystring
// containing 'q=expected+terms' responds, 'cy.wait' will resolve
cy.wait('@search')

Using the yielded object

Using cy.wait() on a cy.intercept() route alias yields an interception object which represents the request/response cycle:

cy.wait('@someRoute').then((interception) => {
  // 'interception' is an object with properties
  // 'id', 'request' and 'response'
})

You can chain .its() and .should() to assert against request/response cycles:

// assert that a request to this route
// was made with a body that included 'user'
cy.wait('@someRoute').its('request.body').should('include', 'user')

// assert that a request to this route
// received a response with HTTP status 500
cy.wait('@someRoute').its('response.statusCode').should('eq', 500)

// assert that a request to this route
// received a response body that includes 'id'
cy.wait('@someRoute').its('response.body').should('include', 'id')

Waiting on errors

You can use cy.wait() to wait on requests that end with network errors:

cy.intercept('GET', '/should-err', { forceNetworkError: true }).as('err')

// assert that this request happened
// and that it ended in an error
cy.wait('@err').should('have.property', 'error')

Stubbing a response

With a string

// requests to '/update' will be fulfilled
// with a body of "success"
cy.intercept('/update', 'success')

With a fixture

// requests to '/users.json' will be fulfilled
// with the contents of the "users.json" fixture
cy.intercept('/users.json', { fixture: 'users.json' })

With a StaticResponse object

A StaticResponse object represents a response to an HTTP request, and can be used to stub routes:

const staticResponse = {
  /* some StaticResponse properties here... */
}

cy.intercept('/projects', staticResponse)

Stub a response with a JSON body:

cy.intercept('/projects', {
  body: [{ projectId: '1' }, { projectId: '2' }],
})

Stub headers, status code, and body all at once:

cy.intercept('/not-found', {
  statusCode: 404,
  body: '404 Not Found!',
  headers: {
    'x-not-found': 'true',
  },
})

See also StaticResponse objects.

Using the routeHandler function

By specifying a routeHandler function as the last argument to cy.intercept, you'll have access to the entire request-response session, enabling you to modify the outgoing request, manipulate the real response, make assertions, etc.

The routeHandler takes the incoming HTTP request (IncomingHTTPRequest) as the first argument.

cy.intercept('/users*', (req) => {
  /* do something with request and/or response */
})

Asserting on a request

cy.intercept('POST', '/organization', (req) => {
  expect(req.body).to.include('Acme Company')
})

Modifying an outgoing request

You can use the request handler callback to modify the intercepted request object before it is sent.

// set the request body to something different
// before it's sent to the destination
cy.intercept('POST', '/login', (req) => {
  req.body = 'username=janelane&password=secret123'
})

// dynamically set the alias
cy.intercept('POST', '/login', (req) => {
  req.alias = 'login'
})

Adding a header to an outgoing request

You can add a header to an outgoing request, or modify an existing header

cy.intercept('/req-headers', (req) => {
  req.headers['x-custom-headers'] = 'added by cy.intercept'
})

Note: the new header will NOT be shown in the browser's Network tab, as the request has already left the browser. You can still confirm the header was added by waiting on the intercept as shown below:

Waiting on the intercept

cy.intercept('/req-headers', (req) => {
  req.headers['x-custom-headers'] = 'added by cy.intercept'
}).as('headers')

// the application makes the call ...
// confirm the custom header was added
cy.wait('@headers')
  .its('request.headers')
  .should('have.property', 'x-custom-headers', 'added by cy.intercept')

Add, modify or delete a header to all outgoing requests

You can add, modify or delete a header to all outgoing requests using a beforeEach() in the cypress/support/index.js file

// cypress/support/index.ts

beforeEach(() => {
  cy.intercept(
    { url: 'http://localhost:3001/**', middleware: true },
    // Delete 'if-none-match' header from all outgoing requests
    (req) => delete req.headers['if-none-match']
  )
})

Dynamically stubbing a response

You can use the req.reply() function to dynamically control the response to a request.

cy.intercept('/billing', (req) => {
  // functions on 'req' can be used to
  // dynamically respond to a request here

  // send the request to the destination server
  req.reply()

  // respond to the request with a JSON object
  req.reply({ plan: 'starter' })

  // send the request to the destination server
  // and intercept the response
  req.continue((res) => {
    // 'res' represents the real destination's response
    // See "Intercepting a response" for more details and examples
  })
})

See "Intercepted requests" for more information on the req object and its properties and methods.

Returning a Promise

If a Promise is returned from the route callback, it will be awaited before continuing with the request.

cy.intercept('POST', '/login', (req) => {
  // you could asynchronously fetch test data...
  return getLoginCredentials().then((credentials) => {
    // ...and then, use it to supplement the outgoing request
    req.headers['authorization'] = credentials
  })
})

Passing a request to the next request handler

If req.reply() or req.continue() is not explicitly called inside of a request handler, requests will pass to the next request handler until none are left.

// you could have a top-level middleware handler that
// sets an auth token on all requests
// but remember setting `middleware: true` will
// cause this to always be called first
cy.intercept('http://api.company.com/', { middleware: true }, (req) => {
  req.headers['authorization'] = `token ${token}`
})

// and then have another handler that
// more narrowly asserts on certain requests
cy.intercept('POST', 'http://api.company.com/widgets', (req) => {
  expect(req.body).to.include('analytics')
})

// a POST request to http://api.company.com/widgets would hit both
// of those callbacks, middleware first, then the request would be
// sent out with the modified request headers to the
// real destination

Intercepting a response

Inside of a callback passed to req.continue(), you can access the destination server's real response.

cy.intercept('/integrations', (req) => {
  // req.continue() with a callback will send the request to
  // the destination server
  req.continue((res) => {
    // 'res' represents the real destination response
    // you can manipulate 'res' before it's sent to the browser
  })
})

See "Intercepted responses" for more information on the res object. See "Controlling the outbound request with req.continue()" for more information about req.continue().

Asserting on a response

cy.intercept('/projects/2', (req) => {
  req.continue((res) => {
    expect(res.body).to.include('My Project')
  })
})

Returning a Promise

If a Promise is returned from the route callback, it will be awaited before sending the response to the browser.

cy.intercept('/users', (req) => {
  req.continue((res) => {
    // the response will not be sent to the browser until
    // 'waitForSomething()' resolves
    return waitForSomething()
  })
})

Throttle or delay response all incoming responses

You can throttle or delay all incoming responses using a beforeEach() in the cypress/support/index.js file

// cypress/support/index.ts

// Throttle API responses to simulate real-world conditions
cy.intercept(
  {
    url: 'http://localhost:3001/**',
    middleware: true,
  },
  (req) => {
    req.on('response', (res) => {
      // Throttle the response to 1 Mbps to simulate a
      // mobile 3G connection
      res.setThrottle(1000)
    })
  }
)

Request/Response Modification with routeHandler

Specify routeHandler as the last argument to modify the outgoing request, stub a response, make assertions, etc.

If a function is passed as the routeHandler, it will be called with the intercepted HTTP request:

cy.intercept('/api', (req) => {
  // do something with the intercepted request
})

From here, you can do several things with the intercepted request:

  • modify and make assertions on the request like its body, headers, URL, method, etc. (example)
  • stub out the response without interacting with a real back-end (example
  • pass the request through to its destination and modify or make assertions on the real response on its way back (example)
  • attach listeners to various events on the request (example)

Asserting on a request

You can use the request handler callback to make an assertion on the intercepted request object before it is sent.

// match requests to create a user
cy.intercept('POST', '/users', (req) => {
  // make an assertion on the payload contents
  expect(req.body).to.include('Peter Pan')
})

Controlling the outgoing request

The outgoing request, including its body, headers, etc., can be modified before it's sent.

// modify the request body before it's sent to its destination
cy.intercept('POST', '/users', (req) => {
  req.body = {
    name: 'Peter Pan',
  }
})

// add a header to an outgoing request
cy.intercept('POST', '/users', (req) => {
  req.headers['x-custom-header'] = 'added by cy.intercept'
})

// modify an existing header
cy.intercept('POST', '/users', (req) => {
  req.headers['authorization'] = 'Basic YWxhZGRpbjpvcGVuc2VzYW1l'
})

Verifying the request modification

cy.intercept('POST', '/users', (req) => {
  req.headers['x-custom-header'] = 'added by cy.intercept'
}).as('createUser')

cy.get('button.save').click()
// you can see the headers in the console output by selecting
// this line in the command log:
cy.wait('@createUser')
  // ...or make an assertion:
  .its('request.headers')
  .should('have.property', 'x-custom-header', 'added by cy.intercept')

Controlling the response

The intercepted request passed to the route handler (hereafter referred to as req, though you can use any name) contains methods to dynamically control the response to a request:

  • req.reply() - stub out a response requiring no dependency on a real back-end
  • req.continue() - modify or make assertions on the real response
  • req.destroy() - destroy the request and respond with a network error
  • req.redirect() - respond to the request with a redirect to a specified location
  • req.on() - modify the response by attaching to events

Stubbing out a response (req.reply()):

req.reply() takes a StaticResponse object as the first argument:

// stub out the response without interacting with a real back-end
cy.intercept('POST', '/users', (req) => {
  req.reply({
    headers: {
      Set-Cookie: 'newUserName=Peter Pan;'
    },
    statusCode: 201,
    body: {
      name: 'Peter Pan'
    },
    delay: 10, // milliseconds
    throttleKbps: 1000, // to simulate a 3G connection
    forceNetworkError: false // default
  })
})

// stub out a response body using a fixture
cy.intercept('GET', '/users', (req) => {
  req.reply({
    statusCode: 200, // default
    fixture: 'users.json'
  })
})

See StaticResponse objects below for more information.

The reply method also supports shorthand to avoid having to specify a StaticResponse object:

// equivalent to `req.reply({ body })`
req.reply(body)

// equivalent to `req.reply({ body, headers })`
req.reply(body, headers)

// equivalent to `req.reply({ statusCode, body, headers})`
req.reply(statusCode, body, headers)

See also Providing a stub response with req.reply()

Modifying the real response (continue):

The continue method accepts a function which is passed an object representing the real response being intercepted on its way back to the client (your front-end application).

// pass the request through and make an assertion on
// the real response
cy.intercept('POST', '/users', (req) => {
  req.continue((res) => {
    expect(res.body).to.include('Peter Pan')
  })
})

See also Controlling the outbound request with req.continue()

Responding with a network error (destroy):

// dynamically destroy the request and
// respond with a network error
cy.intercept('POST', '/users', (req) => {
  if (mustDestroy(req)) {
    req.destroy()
  }

  function mustDestroy(req) {
    // code that determines whether to force a network error
    // based on the contents of `req`
  }
})

Responding with a new location (redirect):

// respond to this request with a redirect to a new 'location'
cy.intercept('GET', '/users', (req) => {
  // statusCode defaults to `302`
  req.redirect('/customers', 301)
})

Responding by listening to events (on):

cy.intercept('GET', '/users', (req) => {
  req.on('before:response', (res) => {
    // do something when the `before:response` event is triggered
  })
})
cy.intercept('POST', '/users', (req) => {
  req.on('response', (res) => {
    // do something when the `response` event is triggered
  })
})

See example for throttling a response See more examples of events

Returning a Promise

If a Promise is returned from the route callback, it will be awaited before continuing with the request.

cy.intercept('POST', '/users', (req) => {
  // asynchronously fetch test data
  return getAuthToken().then((token) => {
    // ...and apply it to the outgoing request
    req.headers['Authorization'] = `Basic ${token}`
  })
})

cy.intercept('POST', '/users', (req) => {
  req.continue((res) => {
    // the response will not be sent to the browser until
    // `waitForSomething()` resolves:
    return waitForSomething()
  })
})

Stubbing a response with a string

// requests to create a user will be fulfilled
// with a body of 'success'
cy.intercept('POST', '/users', 'success')
// { body: 'sucess' }

Intercepted requests

If a function is passed as the handler for a cy.intercept(), it will be called with the first argument being an object that represents the intercepted HTTP request:

cy.intercept('/api', (req) => {
  // `req` represents the intercepted HTTP request
})

From here, you can do several things with the intercepted request:

  • you can modify and assert on the request's properties (body, headers, URL, method...)
  • the request can be sent to the real upstream server
    • optionally, you can intercept the response from this
  • a response can be provided to stub out the request
  • listeners can be attached to various events on the request

Request object properties

The request object (req) has several properties from the HTTP request itself. All of the following properties on req can be modified except for httpVersion:

{
  /**
   * The body of the request.
   * If a JSON Content-Type was used and the body was valid JSON,
   * this will be an object.
   * If the body was binary content, this will be a buffer.
   */
  body: string | object | any
  /**
   * The headers of the request.
   */
  headers: { [key: string]: string }
  /**
   * Request HTTP method (GET, POST, ...).
   */
  method: string
  /**
   * Request URL.
   */
  url: string
  /**
   * URL query string as object.
   */
  query: Record<string, string|number>
  /**
   * The HTTP version used in the request. Read only.
   */
  httpVersion: string
}

req also has some optional properties which can be set to control Cypress-specific behavior:

{
  /**
   * If provided, the number of milliseconds before an upstream
   * response to this request will time out and cause an error.
   * By default, `responseTimeout` from config is used.
   */
  responseTimeout?: number
  /**
   * Set if redirects should be followed when this request is made.
   * By default, requests will not follow redirects before
   * yielding the response (the 3xx redirect is yielded).
   */
  followRedirect?: boolean
  /**
   * If set, `cy.wait` can be used to await the request/response
   * cycle to complete for this request via `cy.wait('@alias')`.
   */
  alias?: string
}

Any modifications to the properties of req will be persisted to other request handlers, and finally merged into the actual outbound HTTP request.

Controlling the outbound request with req.continue()

Calling req.continue() without any argument will cause the request to be sent outgoing, and the response will be returned to the browser after any other listeners have been called. For example, the following code modifies a POST request and then sends it to the upstream server:

cy.intercept('POST', '/submitStory', (req) => {
  req.body.storyName = 'some name'
  // send the modified request and skip any other
  // matching request handlers
  req.continue()
})

If a function is passed to req.continue(), the request will be sent to the real upstream server, and the callback will be called with the response once the response is fully received from the server. See "Intercepted responses"

Note: calling req.continue() will stop the request from propagating to the next matching request handler in line. See "Interception lifecycle" for more information.

Providing a stub response with req.reply()

The req.reply() function can be used to send a stub response for an intercepted request. By passing a string, object, or StaticResponse to req.reply(), the request can be preventing from reaching the destination server.

For example, the following code stubs out a JSON response from a request interceptor:

cy.intercept('/billing', (req) => {
  // dynamically get billing plan name at request-time
  const planName = getPlanName()
  // this object will automatically be JSON.stringified and
  // sent as the response
  req.reply({ plan: planName })
})

Instead of passing a plain object or string to req.reply(), you can also pass a StaticResponse object. With a StaticResponse, you can force a network error, delay/throttle the response, send a fixture, and more.

For example, the following code serves a dynamically chosen fixture with a delay of 500ms:

cy.intercept('/api/users/*', async (req) => {
  // asynchronously retrieve fixture filename at request-time
  const fixtureFilename = await getFixtureFilenameForUrl(req.url)
  req.reply({
    fixture: fixtureFilename,
    delay: 500,
  })
})

See the StaticResponse documentation for more information on stubbing responses in this manner.

req.reply() shorthand

req.reply() also supports shorthand, similar to res.send(), to avoid having to specify a StaticResponse object:

// equivalent to `req.reply({ body })`
req.reply(body)

// equivalent to `req.reply({ body, headers })`
req.reply(body, headers)

// equivalent to `req.reply({ statusCode, body, headers})`
req.reply(statusCode, body, headers)

Convenience functions

There are also two convenience functions available on req:

{
  /**
   * Destroy the request and respond with a network error.
   */
  destroy(): void
  /**
   * Respond to this request with a redirect to a new 'location'.
   * @param statusCode HTTP status code to redirect with. Default: 302
   */
  redirect(location: string, statusCode?: number): void
}

See examples in the Controlling the response section

Note: calling req.reply() will end the request phase and stop the request from propagating to the next matching request handler in line. See "Interception lifecycle" for more information.

Request events

For advanced use, several events are available on req, that represent different stages of the Interception lifecycle.

By calling req.on, you can subscribe to different events:

cy.intercept('/shop', (req) => {
  req.on('before:response', (res) => {
    /**
     * Emitted before `response` and before any `req.continue`
     * handlers. Modifications to `res` will be applied to the
     * incoming response. If a promise is returned, it will be
     * awaited before processing other event handlers.
     */
  })

  req.on('response', (res) => {
    /**
     * Emitted after `before:response` and after any
     * `req.continue` handlers - before the response is sent
     * to the browser. Modifications to `res` will be applied
     * to the incoming response. If a promise is returned, it
     * will be awaited before processing other event handlers.
     */
  })

  req.on('after:response', (res) => {
    /**
     * Emitted once the response to a request has finished
     * sending to the browser. Modifications to `res` have no
     * impact. If a promise is returned, it will be awaited
     * before processing other event handlers.
     */
  })
})

See "Intercepted responses" for more details on the res object yielded by before:response and response. See "Interception lifecycle" for more details on request ordering.

Intercepted responses

The response can be intercepted in two ways:

  • by passing a callback to req.continue() within a request handler
  • by listening for the before:response or response request events (see "Request events")

The response object, res, will be passed as the first argument to the handler function:

cy.intercept('/url', (req) => {
  req.on('before:response', (res) => {
    // this will be called before any `req.continue` or
    // `response` handlers
  })

  req.continue((res) => {
    // this will be called after all `before:response`
    // handlers and before any `response` handlers
    // by calling `req.continue`, we signal that this
    // request handler will be the last one, and that
    // the request should be sent outgoing at this point.
    // for that reason, there can only be one
    // `req.continue` handler per request.
  })

  req.on('response', (res) => {
    // this will be called after all `before:response`
    // handlers and after the `req.continue` handler
    // but before the response is sent to the browser
  })
})

Response object properties

The response object (res) yielded to response handlers has several properties from the HTTP response itself. All of the following properties on res can be modified:

PropertyDescription
bodyresponse body (object, string, ArrayBuffer)
headersresponse headers (object)
statusCoderesponse status code (number)
statusMessageresponse status message (string)

Note about body: If the response header contains Content-Type: application/json and the body contains valid JSON, this will be an object. And if the body contains binary content, this will be a buffer.

res also has some optional properties which can be set to control Cypress-specific behavior:

PropertyDescription
throttleKbpsMaximum data transfer rate of the response (kilobits/second)
delayMinimum network latency or delay to add to the response time (milliseconds)

Any modifications to the properties of res will be persisted to other response handlers, and finally merged into the actual incoming HTTP response.

Ending the response with res.send()

To end the response phase of the request, call res.send(). Optionally, you can pass a StaticResponse to res.send(), to be merged with the actual response.

When res.send() is called, the response phase will end immediately and no other response handlers will be called for the current request. Here is an example of how res.send() could be used:

cy.intercept('/notification', (req) => {
  req.continue((res) => {
    if (res.body.status === 'failed') {
      // sends a fixture body instead of the existing 'res.body'
      res.send({ fixture: 'success.json' })
    }
  })
})

See the StaticResponse documentation for more information on the format.

res.send() shorthand

res.send() also supports shorthand, similar to req.reply(), to avoid having to specify a StaticResponse object:

// equivalent to `res.send({ body })`
res.send(body)

// equivalent to `res.send({ body, headers })`
res.send(body, headers)

// equivalent to `res.send({ statusCode, body, headers})`
res.send(statusCode, body, headers)

Convenience functions

There are also two convenience functions available on res:

{
  /**
   * Wait for 'delay' milliseconds before sending the
   * response to the client.
   */
  setDelay: (delay: number) => IncomingHttpResponse
  /**
   * Serve the response at 'throttleKbps' kilobytes per second.
   */
  setThrottle: (throttleKbps: number) => IncomingHttpResponse
}

Note: calling res.send() will end the response phase and stop the response from propagating to the next matching response handler in line. See "Interception lifecycle" for more information.

StaticResponse objects

A StaticResponse represents a stubbed response to an HTTP request. You can supply a StaticResponse to Cypress in 3 ways:

  • Directly to cy.intercept() as staticResponse, to stub a response to a route: cy.intercept('/url', staticResponse)
  • To req.reply(), to stub a response from a request handler: req.reply(staticResponse)
  • To res.send(), to stub a response from a response handler: res.send(staticResponse)

The following properties are available on StaticResponse. All properties are optional:

OptionDescription
fixtureServe a fixture as the HTTP response body
bodyServe a static response body (object, string, ArrayBuffer)
headersHTTP response headers
statusCodeHTTP response status code
forceNetworkErrorForce an error by destroying the browser connection
delayMinimum network latency or delay to add to the response time (milliseconds)
throttleKbpsMaximum data transfer rate of the response (kilobits/second)

See "Stubbing a response with a StaticResponse object" for examples of stubbing with cy.intercept().

Interception lifecycle

The lifecycle of a cy.intercept() interception begins when an HTTP request is sent from your app that matches one or more registered cy.intercept() routes. From there, each interception has two phases: request and response.

cy.intercept() routes are matched in reverse order of definition, except for routes which are defined with { middleware: true }, which always run first. This allows you to override existing cy.intercept() declarations by defining an overlapping cy.intercept():

Middleware Algorithm

Request phase

The following steps are used to handle the request phase.

  1. Start with the first matching route according to the above algorithm (middleware first, followed by handlers in reverse order).
  2. Was a handler (body, StaticResponse, or function) supplied to cy.intercept()? If not, continue to step 7.
  3. If the handler was a body or StaticResponse, immediately end the request with that response.
  4. If the handler was a function, call the function with req, the incoming request, as the first argument. See "Intercepted requests" for more information on the req object.
  5. If the handler returned a Promise, wait for the Promise to resolve.
  6. Merge any modifications to the request object with the real request.
  7. If there is another matching cy.intercept(), return to step 2 and continue following steps with that route.
  8. Send the request outgoing to the destination server and end the request phase. The response phase will begin once a response is received.

Response phase

Once the HTTP response is received from the upstream server, the following steps are applied:

  1. Get a list of registered before:response event listeners.
  2. For each before:response listener (if any), call it with the res object.
    • If res.send() is called, end the response phase and merge any passed arguments with the response.
    • If a Promise is returned, await it. Merge any modified response properties with the real response.
  3. If a req.continue() with callback is declared for this route, call the callback with the res object.
    • If res.send() is called, end the response phase and merge any passed arguments with the response.
    • If a Promise is returned, await it. Merge any modified response properties with the real response.
  4. Get a list of registered response event listeners.
  5. For each response listener (if any), call it with the res object.
    • If res.send() is called, end the response phase and merge any passed arguments with the response.
    • If a Promise is returned, await it. Merge any modified response properties with the real response.
  6. Send the response to the browser.
  7. Once the response is complete, get a list of registered after:response event listeners.
  8. For each after:response listener (if any), call it with the res object (minus res.send)
    • If a Promise is returned, await it.
  9. End the response phase.

Glob Pattern Matching URLs

When matching a URL, providing an exact URL to match can be too restrictive. For example, what if you wanted to run your tests on a different host?

// match any request that exactly matches the URL
cy.intercept('https://prod.cypress.io/users')
// matches this: https://prod.cypress.io/users
// ...but not this: https://staging.cypress.io/users
// ...or this: http://localhost/users

Glob pattern matching provides the necessary flexibility:

cy.intercept('/users')
// matches all of these:
//   https://prod.cypress.io/users
//   https://staging.cypress.io/users
//   http://localhost/users

cy.intercept('/users?_limit=+(3|5)')
// matches all of these:
//   https://prod.cypress.io/users?_limit=3
//   http://localhost/users?_limit=5

Cypress.minimatch

Under the hood, Cypress uses the minimatch library for glob matching and provides access to it via the Cypress global. This enables you to test your pattern in the Test Runner browser console.

You can invoke the Cypress.minimatch with just two arguments - the URL (string) and the pattern (string), respectively - and if it yields true, then you have a match!

// executed in the Test Runner browser console:
Cypress.minimatch('http://localhost/users?_limit=3', '/users?_limit=+(3|5)')
// true
Cypress.minimatch('http://localhost/users?_limit=5', '/users?_limit=+(3|5)')
// true
Cypress.minimatch('http://localhost/users?_limit=7', '/users?_limit=+(3|5)')
// false

minimatch options

You can also pass in options (object) as the third argument, one of which is debug which if set to true, will yield verbose output that could help you understand why your pattern isn't working as you expect:

Cypress.minimatch('http://localhost/users?_limit=3', '/users?_limit=+(3|5)', {
  debug: true,
})
// true (plus debug messages)

Comparison to cy.route()

Unlike cy.route(), cy.intercept():

  • can intercept all types of network requests including Fetch API, page loads, XMLHttpRequests, resource loads, etc.
  • does not require calling cy.server() before use - in fact, cy.server() does not influence cy.intercept() at all.
  • does not have method set to GET by default, but intercepts * methods.

cy.intercept() and request caching

cy.intercept() intercepts requests at the network layer. This can cause confusion when trying to intercept a request that has already been cached by the browser. If a request is served from the browser cache, it will never hit the network layer, and cy.intercept() will never fire.

To see if this is affecting your app, check the Developer Tools. In the following example, all of the requests circled in red have been served from cache, and will not send an HTTP request. Thus, they cannot be intercepted by cy.intercept():

Screenshot of Chrome DevTools showing cached responses.

If you would like to intercept resources that normally send cache headers, here are some workarounds:

  • Turn off cache headers on your development server when in testing mode.
  • Disable caching on responses by adding a top-level cy.intercept() that removes cache headers from desired requests. For example:
    beforeEach(() => {
      cy.intercept(
        'https://api.example.com/**/*',
        { middleware: true },
        (req) => {
          req.on('before:response', (res) => {
            // force all API responses to not be cached
            res.headers['cache-control'] = 'no-store'
          })
        }
      )
    })
    
  • Chromium-family browsers only: Use remote:debugger:protocol to disable cache entirely. For more information, see this comment on issue #14459

History

VersionChanges
7.6.0Added query option to req (The incoming request object yielded to request handler functions).
7.0.0Removed matchUrlAgainstPath option from RouteMatcher, reversed handler ordering, added request events, removed substring URL matching, removed cy.route2 alias, added middleware RouteMatcher option, renamed res.delay() to res.setDelay() and res.throttle() to res.setThrottle().
6.4.0Renamed delayMs property to delay (backwards-compatible).
6.2.0Added matchUrlAgainstPath option to RouteMatcher.
6.0.0Renamed cy.route2() to cy.intercept().
6.0.0Removed experimentalNetworkStubbing option and made it the default behavior.
5.1.0Added experimental cy.route2() command under experimentalNetworkStubbing option.

See also