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Configuration

On any fetch-mock instance, set configuration options directly on the fetchMock.config object. e.g.

const fetchMock = require('fetch-mock');
fetchMock.config.sendAsJson = false;

Available options​

Options marked with a † can also be overridden for individual calls to .mock(matcher, response, options) by setting as properties on the options parameter

sendAsJson†​

{Boolean} default: true

Always convert objects passed to .mock() to JSON strings before building reponses. Can be useful to set to false globally if e.g. dealing with a lot of ArrayBuffers. When true the Content-Type: application/json header will also be set on each response.

includeContentLength†​

{Boolean} default: true

Sets a Content-Length header on each response.

fallbackToNetwork​

{Boolean|String} default: false

  • true: Unhandled calls fall through to the network
  • false: Unhandled calls throw an error
  • 'always': All calls fall through to the network, effectively disabling fetch-mock.

overwriteRoutes†​

{Boolean} default: undefined

Configures behaviour when attempting to add a new route with the same name (or inferred name) as an existing one

  • undefined: An error will be thrown
  • true: Overwrites the existing route
  • false: Appends the new route to the list of routes

matchPartialBody​

{Boolean} default: false

Match calls that only partially match a specified body json. Uses the is-subset library under the hood, which implements behaviour the same as jest's .objectContaining() method.

warnOnFallback​

{Boolean} default: true

Print a warning if any call is caught by a fallback handler (set using catch(), spy() or the fallbackToNetwork option)

Custom fetch implementations​

fetch, Headers, Request, Response can all be set on the configuration object, allowing fetch-mock to mock any implementation if you are not using the default one for the environment.