Mock Exports Loader

👉中文

MockExportsLoader converts exports of given module to empty functions by analyze module exports and type definition files (some compressed commonjs code may not be easy to extract exports by static analyze, thus we can use it's type definitions to extract exports).

Sometimes we may need to build special package for special purpose, and some module is not truly executed but cannot be shaked due to some side effects; we may use null-loader or { alias: { xx: false } } to shake the module but the code may be broken after the shaking. MockExportsLoader is for such case that we can automatically 'mock' those modules and provide empty function like what we do for test.

Roadmap

✅ Analyze exports by code

✅ Analyze exports by type definition files

🔳 Analyze exports type, distinguish function and const object or value

🔳 Provide type definition files for mock file

How to use

Install

npm i --save-dev mock-exports-loader

Usage

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /target_module/,
        loader: 'mock-exports-loader',
        options: {
          parseFromType: false,
          generateDefault: false,
          createMocks: () => ({}),
        },
      }
    ],
  },
  // ...
}

Loader Options

parseFromType

boolean | undefined, default is false

Whether to extract exports from type defintion file, recommend for compressed non-es6 module with type definitions. Support auto detect @type/xxx for lib xxx, e.g. for lib module-a, it will automatically search @type/module-a if module-a has no types/typing field in package.json.

{
  test: /module-a/,
  loader: 'mock-exports-loader',
  options: {
    parseFromType: true,
  },
}

generateDefault

boolean | undefined, default is false

Whether to merge all named exports to module's default export. e.g. for module fs-extra, we can use either import fs from 'fs-extra' fs.readFileSync or import { readFileSync } from 'fs-extra',but automatic mock will create an empty default export due to the current static code analysis logic.

// ...
module.exports.readFileSync = function () {};
// ...
module.exports.default = function () {};

Set generateDefault to true to make the mock fs object work as expected:

// ...
module.exports.readFileSync = function () {};
// ...
module.exports.default = {
  // ...
  readFileSync: function () {};
  // ...
};

createMocks

(() => object) | undefined, default is undefined

There could be some exports cannot be recognized or some constants mistakenly converted to empty function. We could provides a createMocks function to fix it.

{
  test: /module-a/,
  loader: 'mock-exports-loader',
  options: {
    createMocks: () => ({ CONST_VALUE: 3 }),
  },
}

mock Result:

module.exports.CONST_VALUE = 3;

Known Issues

1. Due to current logic of static code analysis, it's not easy to distinguish function export and value object export. All exports will be convert to empty function, you must provide a createMocks to provide the correct constant exports.