sekoyo / mockster

A library for mocking fetch responses.

Mockster

A library for mocking fetch responses.

Install

npm i --save mockster

import mockster from 'mockster';

Note: window.fetch is automatically mocked when including this library. It's a good idea to only include mocks in a mock build so this usually isn't an issue. If you need them the library also exports fetchHook and fetchUnhook, as well as fetchUnmock(url, method).

Tip: You can include mocks in a webpack build with no extra config. Create a mocks/index.js file at your root and run npm start -- mocks.

Usage

Supported methods: delete, get, patch, post, put.

mockster.get('/film/:title?rating=:rating', (url, params) => {
  // params.title = 'batman'
  // params.rating = '8'
  return { something: 'to return' };
});

fetch('/film/batman?rating=8');

You can also return error responses using status and body, as well as a headers object if your response isn't JSON.

mockster.post('/project/create', (url, params, options) => {
  if (options.body.name === 'Farting investigation') {
    return {
      status: 409,
      body: 'That project already exists',
    };
  }

  // An object without a `body` property is considered to be the body,
  // and the status will be 200 'OK'.
  return {
    ...options.body,
    id: '3250235H6',
  };
});

fetch('/project/create', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    name: 'Hubot',
  }),
});

You can also return a Promise if you want to delay the response or do async work:

mockster.get('/hello', () =>
  new Promise((resolve) => {
    setTimeout(() => resolve({ hello: 'world' }), 300);
  }));

Parameters

Parameters are avaiable in the second arguments (params). URLs support params, splats, and optional segments.

Example	Description
:name	a parameter to capture from the route up to /, ?, or end of string
*splat	a splat to capture from the route up to ? or end of string
()	Optional group that doesn't have to be part of the query. Can contain nested optional groups, params, and splats
anything else	free form literals

Some examples:

• /some/(optional/):thing
• /users/:id/comments/:comment/rating/:rating
• /*a/foo/*b
• /books/*section/:title
• /books?author=:author&subject=:subject

Matching based on options

It is also possible to match based on options as well as the URL. A deep equal will be performed on the options you wish to compare:

mockster.post('project/create', (url, params, options) => {
  return 'your response';
}, {
  body: {
    name: 'Billy Bob',
  }
});

Not all options will pass an equality check (for example FormData), to this effect options can also be a function:

mockster.post('project/create', (url, params, options) => {
  return 'your response';
}, options => options.body.name.startsWith('Billy'));