inject-loader

4.0.1 verified Sat Apr 25 auth: no javascript

A Webpack loader for injecting mock dependencies into modules under test. Current stable version 4.0.1, maintained steadily. It wraps all require statements in a module so you can substitute them during testing. Unlike proxyquire or rewire, it works as a Webpack inline loader, making it seamless in Webpack-based projects. Supports Webpack 1 through 4. Particularly useful for unit testing where you need to mock internal dependencies of a module before it executes.

Common errors

error TypeError: inject_loader is not a function ↓

cause Using inject-loader as a regular module instead of an inline loader.

fix

Use require('inject-loader!./MyModule') instead of require('inject-loader')(...).

error Module not found: Error: Can't resolve 'inject-loader' ↓

cause inject-loader not installed or not in node_modules.

fix

Run 'npm install --save-dev inject-loader'.

error Critical dependency: require function is used in a way in which dependencies cannot be statically extracted ↓

cause Webpack 4 warns about dynamic requires; inject-loader uses dynamic require internally.

fix

This warning is expected and usually harmless. Suppress with webpack config stats: 'warningsFilter: /Critical dependency/'.

error Inject loader only works with CommonJS modules (module.exports/require). ↓

cause Using ES module syntax (import/export) in the injected module.

fix

Ensure the module under test uses CommonJS require/module.exports, or use a babel transform to convert.

Warnings

gotcha You must use the inline loader syntax 'inject-loader!./module' in your require/import statements. Using inject-loader as a regular module and calling it as a function will not work. ↓

fix Use 'require("inject-loader!./module")' instead of 'require("inject-loader").(./module)'.

deprecated Webpack 1 and 2 support is deprecated. The loader still works but no longer actively tested. ↓

fix Upgrade to Webpack 3 or 4 for official support.

gotcha The loader wraps all require statements by default. If you want to exclude certain dependencies, you must provide flags (not documented in readme). ↓

fix Check loader options or use flags as described in the example folder: require('inject-loader?exclude=events!./module').

breaking In v4, the loader now returns a single injector function instead of an object with inject method. ↓

fix Call the result directly: const module = require('inject-loader!./module')({...}) instead of require('inject-loader!./module').inject({...}).

Install

npm install inject-loader

yarn add inject-loader

pnpm add inject-loader

Imports

inject-loader
wrong
```
const inject = require('inject-loader'); const MyModuleInjector = inject('./MyModule');
```
correct
```
import MyModuleInjector from 'inject-loader!./MyModule';
```
inject-loader is used as an inline Webpack loader, not a regular module. The correct usage is to prefix the module path with 'inject-loader!' in the require/import statement.

inject-loader (CommonJS)

wrong

const MyModuleInjector = require('inject-loader')( './MyModule' );

correct

const MyModuleInjector = require('inject-loader!./MyModule');

When using CommonJS, still use the inline loader syntax in the require path.

injector function

wrong

const MyModule = MyModuleInjector.inject({ 'lib/dispatcher': DispatcherMock });

correct

const MyModule = MyModuleInjector({ 'lib/dispatcher': DispatcherMock, 'events': EventsMock, 'lib/handle_action': HandleActionMock });

The loader returns a function that accepts an object mapping dependency paths to mock modules.

Quickstart

Shows how to require a module via inject-loader inline and inject mock dependencies.

// Example test using inject-loader with Jest
const MyModuleInjector = require('inject-loader!./MyModule');
const DispatcherMock = { register: jest.fn() };
const EventsMock = { EventEmitter: jest.fn() };
const HandleActionMock = jest.fn();
const MyModule = MyModuleInjector({
  'lib/dispatcher': DispatcherMock,
  'events': EventsMock,
  'lib/handle_action': HandleActionMock
});
// Now MyModule uses the mocked dependencies
DispatcherMock.register.mock.calls.length; // 1