Error responses

An error response is just a response with a 4xx or 5xx status code and, optionally, an error payload. In Mock Config you can describe one either statically through settings, or dynamically from a resolver.

Error As A Stub

For a route that should always fail, set the status code through the third settings argument and return the error payload as the response.

rest.get(
  '/users/1',
  {
    error: 'Not Found'
  },
  {
    status: 404
  }
);

Every GET /users/1 request receives the payload with a 404 status code. This is the simplest way to describe a known error scenario.

Error From A Resolver

When whether the request fails depends on its data, decide inside a resolver and set the status code with setStatusCode.

rest.get<{ params: { id: string } }>('/users/:id', ({ request, setStatusCode }) => {
  if (request.params.id === '1') {
    setStatusCode(404);

    return {
      error: 'Not Found'
    };
  }

  return {
    id: request.params.id,
    name: 'John'
  };
});

Here GET /users/1 responds with a 404, while any other id returns a normal user. The resolver reads the request, sets the status code, and returns the matching payload.

Errors And Matchers

You can also describe an error as its own scenario with a Matcher, keeping each response static. This pairs well with a default success stub.

import { exists, rest } from 'mock-config-server';

const routes = [
  rest.get('/users', [{ id: 1, name: 'John' }], {
    match: {
      headers: {
        authorization: exists()
      }
    }
  }),
  rest.get(
    '/users',
    {
      error: 'Unauthorized'
    },
    {
      status: 401
    }
  )
];

Here a request with an authorization header matches the first, more specific stub, while every other GET /users falls back to the 401 error.