babel-plugin-rewire

A Babel plugin that adds the ability to rewire module dependencies.

It is inspired by rewire.js and transfers its concepts to es6 using babel.

It is useful for writing tests, specifically to mock the dependencies of the module under test.

Therefore for each module it adds and exports the methods __GetDependency__, __Rewire__, and __ResetDependency__. For compatibility reasons with rewire.js, the methods __get__ and __set__ are exported as well. From version 1.0.0-rc-7 on calls to __set__ will return a revert function like rewire.js.

These methods allow you to rewire the module under test. Furthermore in case of a default export these methods are assigned to the existing default export, except for default exports of primitive types (boolean, number, string, ...).

An additional object named __RewireAPI__ is exported as named export as well as a property of the default export. This object itself contains all the functions mentioned above as fields. This enables one to rewire members of the imported module itself without explicitly importing the module (see Handling of default exports below).

ES6 Imports and React

Dependencies from import statements can be rewired

Example

1import ChildComponent from 'child-component-module';
2
3export default class MyFancyWrapperComponent extends React.Component {
4
5  render() {
6    return (<div className="wrapper-style">
7      <ChildComponent {...this.props} />
8    </div>);
9  }
10}

Test Code

1import ComponentToTest from 'my-fancy-wrapper-component-module';
2
3ComponentToTest.__Rewire__('ChildComponent', React.createClass({
4    render: function() { return <div {...this.props}></div>; }
5}));
6....
7
8ComponentToTest.__ResetDependency__('ChildComponent');

Node/browserify require() and top-level var support

Variables declared and initialised at the top level, such as those from require() calls, can be rewired

Example

1var Path = require('path');
2
3var env = 'production';
4
5module.exports = function(name) {
6  return Path.normalise(name);
7}

Test Code

1var Normaliser = require('Normaliser');
2
3Normaliser.__Rewire__('Path', {
4  normalise: (name) => name;
5});
6
7Normaliser.__Rewire__('env', 'testing');
8....
9
10Normaliser.__ResetDependency__('Path');

Named and top level function rewiring

Besides top level variables also top level functions defined in the imported module can be rewired.

When exported functions of a module depend on each other it can be convenient to test them independently. Hence, babel-plugin-rewire allows you to rewire the internal dependencies to exported named functions as shown in the example below.

Be aware, that rewiring a named export does not influence imports of that same export in other modules!

Example

Asuming you have a module TodoOperations.js that internaly uses an asynchronous api to fetch some information

1function fetchToDos() {
2   ...
3   return new Promise(...);
4}
5
6export function filterToDos( filterString ) {
7   return fetchToDos().then( function( todos ) {
8      // Highly fashioned filter function code ...
9      return filteredToDos;
10   });
11}
12
13export function filterAndSortToDos( filterString, sortOrder ) {
14   return fetchToDos( filterString ).then( function( filteredToDos ) { 
15      // Higly fashioned sort function
16      return filteredAndSortedToDos;
17   });
18}

Test Code

In your test you can mock your API-calls to simply return static dummy data like this

1import { filterToDos, filterAndSortToDos, __RewireAPI__ as ToDosRewireAPI } from 'TodoOperations.js';
2
3describe('api call mocking', function() {
4   it('should use the mocked api function', function(done) {
5      ToDosRewireAPI.__Rewire__('fetchToDos', function() {
6         return Promise.resolve(['Test more', 'Refine your tests', 'Tests first rocks']);
7      });
8      filterToDos('Test').then(function(filteredTodos) {
9         //check results
10         done();
11      }).catch((e) => fail());
12      ToDosRewireAPI.__ResetDependency__('fetchToDos');
13   });
14   
15   it('should use the mocked filter function', function(done) {
16      ToDosRewireAPI.__Rewire__('filterToDos', function() {
17         return Promise.resolve( ['02 Test more', '01 Test even more' ] );
18      });
19      filterAndSortToDos('Test', 'asc').then(function(filteredAndSortedTodos) {
20         //check results
21         done();
22      }).catch((e) => fail());
23      ToDosRewireAPI.__ResetDependency__('filterToDos');
24   });
25});

Handling of default exports

If a non primitive default export is present in the imported module, it is enriched with the API-Functions and the API-Object. If no default export is present, the API-Object named __RewireAPI__ becomes the default export of the module.

This object basically supports all the rewire API-Functions as described in the introduction above and allows one to rewire the module without explicitly importing the module itself.

Example

Asuming your imported module does not have a default export specified like in this simple example

1function message() {
2   return 'Hello world';
3}
4
5export function foo() {
6   return message();
7}

Test Code

In your test you would use the default exported API-Object to rewire the function message of the imported module like this

1import FooModule from 'foo.js';
2import { foo, __RewireAPI__ as FooModuleRewireAPI } from 'foo.js';
3
4describe('module default export test', function() {
5   it('should demonstrate the default exported rewire api', function() {
6      expect( foo() ).to.equal('Hello world');
7      FooModule.__Rewire__('message', function() {
8         return 'my message';
9      });
10      expect( foo() ).to.equal('my message');
11      FooModule.__ResetDependency__('message');
12   });
13   
14   it('should demonstrate the rewire apis named export', function() {
15      expect( foo() ).to.equal('Hello world');
16      FooModuleRewireAPI.__Rewire__('message', function() {
17         return 'my message';
18      });
19      expect( foo() ).to.equal('my message');
20      FooModuleRewireAPI.__ResetDependency__('message');
21   });
22});

Handling of async functions

Rewiring of async functions works as one would expect using the same API as for other rewires for both default exports and named exports.

Example

Assuming your imported module consists of the following.

1// api.js
2export default async function asyncApiDefault() {
3   return await asyncApi();
4};
5
6export async function asyncApi() {
7   return await api();
8};
9
10function api() {
11  // Some async API call
12  return Promise.resolve('API Response');
13};

Test Code

In your test you would use the default exported API-Object to rewire the function asyncApiDefault and asyncApi of the imported module like this.

1import { default as asyncApiDefault, asyncApi,  __RewireAPI__ as AsyncApiRewireAPI } from 'api.js';
2describe('async function export test', function() {
3 it('should be able to rewire default async function', function() {
4    return asyncApiDefault().then(response => {
5      expect(response).to.equal('API Response');
6
7      AsyncApiRewireAPI.__set__('asyncApi', function() {
8        return Promise.resolve('Mock API Response');
9      });
10
11      return asyncApiDefault().then(response => {
12        expect(response).to.equal('Mock API Response');
13        AsyncApiRewireAPI.__ResetDependency__('asyncApi');
14      });
15    });
16  });
17
18  it('should be able to rewire non default async function', function() {
19    return asyncApi().then(response => {
20      expect(response).to.equal('API Response');
21
22      AsyncApiRewireAPI.__set__('api', function() {
23        return Promise.resolve('Mock API Response');
24      });
25
26      return asyncApi().then(response => {
27        expect(response).to.equal('Mock API Response');
28        AsyncApiRewireAPI.__ResetDependency__('api');
29      });
30    });
31  });
32});

Resetting all

When "babel-plugin-rewire" is used the global method __rewire_reset_all__ is added. Each time this method is called all rewired dependencies across all modules are reset.

Example

Assuming you have two imported modules:

Module1:

1var value = 'Module1-Original';
2
3export default function getModule2Identifier() {
4	return value;
5}

Module2:

var value = 'Module2-Original';

export default function getModule2Identifier() {
	return value;
}

Test Code

In your test by calling __rewire_reset_all__ all dependencies are reset and you can ensure that no rewired data will harm subsequent tests.

1import getModule1Identifier from './src/Module1.js';
2import getModule2Identifier from './src/Module2.js';
3
4import expect from "expect.js";
5
6describe('__rewire_reset_all__', function () {
7	it('should allow to reset all rewired dependencies', function() {
8		expect(getModule1Identifier()).to.be('Module1-Original');
9		expect(getModule2Identifier()).to.be('Module2-Original');
10
11		getModule1Identifier.__set__('value', 'module1-rewired');
12		getModule2Identifier.__set__('value', 'module2-rewired');
13
14		expect(getModule1Identifier()).to.be('module1-rewired');
15		expect(getModule2Identifier()).to.be('module2-rewired');
16
17		__rewire_reset_all__();
18
19		expect(getModule1Identifier()).to.be('Module1-Original');
20		expect(getModule2Identifier()).to.be('Module2-Original');
21	});
22});

Installation

$ npm install babel-core babel-plugin-rewire

Usage

To use the plugin identify it by its long name "babel-plugin-rewire" or by its abbreviation "rewire". In case you are using rewire.js in the same project you must use the unabbreviated plugin name. Otherwise babel is trying to load rewire.js as a plugin which will cause an error.

Commandline

abbreviated:

$ babel --plugins rewire ..

full plugin name:

$ babel --plugins babel-plugin-rewire ..

With babelrc

You can also specify plugins via the babelrc file:

1{
2  "plugins": ["rewire"]
3}

Whether you're using the command line, JS API, or require hook, this file is honored by babel.

JavaScript API

abbreviated:

1require("babel-core").transform("code", { plugins: ["rewire"] });

full plugin name:

1require("babel-core").transform("code", { plugins: ["babel-plugin-rewire"] });

Require Hook

1require('babel-register')({
2  plugins: ['babel-plugin-rewire']
3})

Webpack

abbreviated:

1{test: /src\/js\/.+\.js$/, loader: 'babel-loader?plugins=rewire' }

full plugin name:

1{test: /src\/js\/.+\.js$/, loader: 'babel-loader?plugins=babel-plugin-rewire' }

Browserify/Babelify

full plugin name:

1var appBundler = browserify({
2    entries: [test.src], // Only need initial file, browserify finds the rest
3}).transform(
4    babelify.configure({
5        plugins: [require('babel-plugin-rewire')]
6    })
7);

Combining with other plugins/tools

istanbul

To integrate babel-plugin-rewire with istanbul, it is recommended to use babel-plugin-istanbul. This babel plugin instruments your code with Istanbul coverage.

It has been reported that the order of plugins are important. Therefore prefer the following order:

1{
2  "plugins": ["istanbul", "rewire"]
3}

For a project integrating karma, babel, babel-plugin-rewire and istanbul please see karma-rewire-istanbul-example

isparta

There are some things to consider when using babel-plugin-rewire together with isparta. Since isparta runs Babel itself it's important to remember to add the same configuration options to it as you would do with Babel. If you forget this you will in some cases see unexpected errors.

If you use .babelrc it's advised that you run your tests with a specific ENV, for example "test", and add the following to your .babelrc. Furthermore in case you use isparta only add the plugin once in the isparta loader and not in the babel loader as well.

1"env": {
2  "test": {
3    "plugins": ["rewire"]
4  }
5}

If you are using isparta together with Webpack you could also do something like this.

1webpack: {
2  isparta: {
3    embedSource: true,
4    noAutoWrap: true,
5    babel: {
6      plugins: 'rewire'
7    }
8  },
9  preLoaders: [
10  ...
11    {
12      test: /\.js$/,
13      include: path.resolve('src/'), //only source under test
14      loader: 'isparta'
15    },
16  ]
17    ...
18}

Examples projects

• es6-library-boilerplate

Release History

• 0.1.0 Initial release
• 0.1.1 Bugfix: moved to peer dependencies
• 0.1.2 Added __set__ and __get__ to provide compatibility with rewire.js
• 0.1.3 Added handling for the export of named declarations like classes or functions
• 0.1.4 Fixed variable handling and used renaming of scope variables. Further removed global identifiers to prevent memory leaks.
• 0.1.5 Fixed regression
• 0.1.6 Support for rewiring top level variables. Added module.exports for non-es6 modules.
• 0.1.7 Fixed regressions from 0.1.6.
• 0.1.8 Ignores destructuring assignments to prevent errors.
• 0.1.9 Removed issues with TDZ and es6.spec.blockScoping optional transformer.
• 0.1.10 Fixed tests.
• 0.1.11 Fixed issues with for-of loops.
• 0.1.12 Updated Plugin Format.
• 0.1.13 Changed rewire specific properties on default export to non-enumerable properties.
• 0.1.14 Added handling for non-enumerable properties to commonjs support. Support for mixed es6 and commonjs support. Handling for primitive types.
• 0.1.15 Added functionality to rewire functions.
• 0.1.16 Fixed variable scope for rewired functions.
• 0.1.17 Fixed variable scoping for var variable declarations.
• 0.1.18 Fixed function scope for rewired functions.
• 0.1.19 Removed debug statements.
• 0.1.20 Added rewiring named exported functions and variables.
• 0.1.21 Improved default export handling, fixed commonjs default exporting, fixed ast nodes resource leaks, improved README.
• 0.1.22 Added support for asynchronous functions
• 0.1.23-beta Improved flow compatibility, Added functionality to work with cyclic dependencies.
• 1.0.0-beta-1 Added support for babel 6, added support for rewiring classes, added support for flow types, added support for rewire.js compatible _with_
• 1.0.0-beta-2 Removed rewire of Object, require
• 1.0.0-beta-3 Removed support for rewiring of globals. Added support for rewiring in combination with assignment and update expressions.
• 1.0.0-beta-4 Updates jsx support in combination with babel 6 but has a regression
• 1.0.0-beta-5 Fixes rewiring of jsx elements. Readme improvements. Test for pass-through like modules.
• 1.0.0-rc-1 Fixes rewiring of switch statements. Readme improvements. Wildcard imports and tdz issues.
• 1.0.0-rc-2 Fixes issues with babelify, React stateless functions as well as flow declarations.
• 1.0.0-rc-3 Added support for ignoring identifiers and support for objects as parameter to _set_
• 1.0.0-rc-4 Support for rewiring to undefined, suppport for should.js and cleaned up package.json.
• 1.0.0-rc-5 Improved support for rewiring JSX-Components. Further improved for working in combination with other plugins.
• 1.0.0-rc-6 Fixed regression which can occur with variable declarators and function expressions. Fixed handling of default exports containing nested functions.
• 1.0.0-rc-7 Added revert function as a return of _set_ calls.
• 1.0.0 Fixed regression with object methods and improved istanbul documentation.
• 1.2.0-rc.1 Add support for babel 7, object spread and revert function from __set__ with object and fixes undefined variable error

Contributors

• speedskater - author and creator of initial release
• Peet - module.exports and top-level var support
• TheSavior - support for non-enumerable rewire properties, support for ignored identifiers
• Rene Saarsoo - support for using objects as parameter to __set__
• PSpSynedra - support for named export and function rewiring and improvements of default imports
• Gustaf Dalemar - support for asynchronous functions
• Spencre Leichty - support for named wildcard exports
• Zhanzhan He - support for wildcard imports
• Kelly Selden - fixed dependencies in package.json
• Sasha Koss - support for rewiring to undefined
• Kevin Canévet - fixed incompatibility with should
• Mike Sherov - added support for for in loops
• Thomas Levy - added support for babel 7
• Malthe Jørgensen - added support for object spread
• Tim Whitbeck - added revert function from __set__ with object
• Dennis E - fixed undefined __$$GLOBAL_REWIRE_REGISTRY__ error

License

The ISC License (ISC)

Copyright (c) 2015, Robert Binna r.binna@synedra.com

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.