Features

• Speeds up TypeScript type checking and ESLint linting (by moving each to a separate process) 🏎
• Supports modern TypeScript features like project references and incremental mode ✨
• Supports Vue Single File Component ✅ 
• Displays nice error messages with the code frame formatter 🌈

Installation

This plugin requires minimum Node.js 10, Webpack 4, TypeScript 2.7 and optionally ESLint 6

• If you depend on Webpack 2, Webpack 3, or TSLint 4, please use version 3 of the plugin.
• If you depend on TypeScript >= 2.1 and < 2.7 or you can't update to Node 10, please use version 4 of the plugin. ```sh # with npm npm install --save-dev fork-ts-checker-webpack-plugin

with yarn

yarn add --dev fork-ts-checker-webpack-plugin

The minimal webpack config (with [ts-loader](https://github.com/TypeStrong/ts-loader))

```js
// webpack.config.js
const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');

module.exports = {
  context: __dirname, // to automatically find tsconfig.json
  entry: './src/index.ts',
  resolve: {
    extensions: [".ts", ".tsx", ".js"],
  },
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        loader: 'ts-loader',
        exclude: /node_modules/,
        options: {
          // disable type checker - we will use it in fork plugin
          transpileOnly: true
        }
      }
    ]
  },
  plugins: [new ForkTsCheckerWebpackPlugin()]
};

Examples how to configure it with babel-loader, ts-loader, eslint and Visual Studio Code are in the examples directory.

Modules resolution

It's very important to be aware that this plugin uses TypeScript's, not webpack's modules resolution. It means that you have to setup tsconfig.json correctly.

It's because of the performance - with TypeScript's module resolution we don't have to wait for webpack to compile files.

To debug TypeScript's modules resolution, you can use tsc --traceResolution command.

ESLint

If you'd like to use ESLint with the plugin, ensure you have the relevant dependencies installed:

# with npm
npm install --save-dev eslint @typescript-eslint/parser @typescript-eslint/eslint-plugin

# with yarn
yarn add --dev eslint @typescript-eslint/parser @typescript-eslint/eslint-plugin

Then set up ESLint in the plugin. This is the minimal configuration:

// webpack.config.js
const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');

module.exports = {
  // ...the webpack configuration
  plugins: [
    new ForkTsCheckerWebpackPlugin({
      eslint: {
        files: './src/**/*.{ts,tsx,js,jsx}' // required - same as command `eslint ./src/**/*.{ts,tsx,js,jsx} --ext .ts,.tsx,.js,.jsx`
      }
    })
  ]
};

You should also have an ESLint configuration file in your root project directory. Here is a sample .eslintrc.js configuration for a TypeScript project:

module.exports = {
  parser: '@typescript-eslint/parser',
  parserOptions: {
    ecmaVersion: 2018,
    sourceType: 'module',
  },
  extends: [
    'plugin:@typescript-eslint/recommended'
  ],
  rules: {
    // place to specify ESLint rules - can be used to overwrite rules specified from the extended configs
    // e.g. "@typescript-eslint/explicit-function-return-type": "off",
  }
};

There's a good explanation on setting up TypeScript ESLint support by Robert Cooper.

Options

This plugin uses cosmiconfig. This means that besides the plugin constructor, you can place your configuration in the:

• "fork-ts-checker" field in the package.json
• .fork-ts-checkerrc file in JSON or YAML format
• fork-ts-checker.config.js file exporting a JS object

Options passed to the plugin constructor will overwrite options from the cosmiconfig (using deepmerge).

Name	Type	Default value	Description
async	boolean	compiler.options.mode === 'development'	If true, reports issues after webpack's compilation is done. Thanks to that it doesn't block the compilation. Used only in the watch mode.
typescript	object or boolean	true	If a boolean, it enables/disables TypeScript checker. If an object, see TypeScript options.
eslint	object	undefined	If undefined, it disables ESLint linter. If an object, see ESLint options.
issue	object	{}	See Issues options.
formatter	string or object or function	codeframe	Available formatters are basic, codeframe and a custom function. To configure codeframe formatter, pass object: { type: 'codeframe', options: { <coderame options> } }.
logger	object	{ infrastructure: 'silent', issues: 'console', devServer: true }	Available loggers are silent, console, and webpack-infrastructure. Infrastructure logger prints additional information, issue logger prints issues in the async mode. If devServer is set to false, errors will not be reported to Webpack Dev Server.

TypeScript options

Options for the TypeScript checker (typescript option object).

Name	Type	Default value	Description
enabled	boolean	true	If true, it enables TypeScript checker.
memoryLimit	number	2048	Memory limit for the checker process in MB. If the process exits with the allocation failed error, try to increase this number.
configFile	string	'tsconfig.json'	Path to the tsconfig.json file (path relative to the compiler.options.context or absolute path)
configOverwrite	object	{ compilerOptions: { skipLibCheck: true, sourceMap: false, inlineSourceMap: false, declarationMap: false } }	This configuration will overwrite configuration from the tsconfig.json file. Supported fields are: extends, compilerOptions, include, exclude, files, and references.
context	string	dirname(configuration.configFile)	The base path for finding files specified in the tsconfig.json. Same as the context option from the ts-loader. Useful if you want to keep your tsconfig.json in an external package. Keep in mind that not having a tsconfig.json in your project root can cause different behaviour between fork-ts-checker-webpack-plugin and tsc. When using editors like VS Code it is advised to add a tsconfig.json file to the root of the project and extend the config file referenced in option configFile.
build	boolean	false	The equivalent of the --build flag for the tsc command.
mode	'readonly' or 'write-tsbuildinfo' or 'write-dts' or 'write-references'	'write-tsbuildinfo'	If you use the babel-loader, it's recommended to use write-references mode to improve initial compilation time. If you use ts-loader, it's recommended to use write-tsbuildinfo mode to not overwrite files emitted by the ts-loader. If you use ts-loader with transpileOnly flag set to true, use 'write-dts to emit the type definition files.
diagnosticOptions	object	{ syntactic: false, semantic: true, declaration: false, global: false }	Settings to select which diagnostics do we want to perform.
extensions	object	{}	See TypeScript extensions options.
profile	boolean	false	Measures and prints timings related to the TypeScript performance.
typescriptPath	string	require.resolve('typescript')	If supplied this is a custom path where TypeScript can be found.

TypeScript extensions options

Options for the TypeScript checker extensions (typescript.extensions option object).

Name	Type	Default value	Description
vue	object or boolean	false	If true, it enables Vue Single File Component support.
vue.enabled	boolean	false	Same as the vue option
vue.compiler	string	'vue-template-compiler'	The package name of the compiler that will be used to parse .vue files. You can use 'nativescript-vue-template-compiler' if you use nativescript-vue

ESLint options

Options for the ESLint linter (eslint option object).

Name	Type	Default value	Description
enabled	boolean	false	If true, it enables ESLint linter. If you set the files option, it will be true by default.
files	string or string[]	This value is required	One or more glob patterns to the files that should be linted. Works the same as the eslint command.
memoryLimit	number	2048	Memory limit for the linter process in MB. If the process exits with the allocation failed error, try to increase this number.
options	object	{}	Options that can be used to initialize ESLint.

Issues options

Options for the issues filtering (issue option object). I could write some plain text explanation of these options but I think code will explain it better:

interface Issue {
  origin: 'typescript' | 'eslint';
  severity: 'error' | 'warning';
  code: string;
  file?: string;
}

type IssueMatch = Partial<Issue>; // file field supports glob matching
type IssuePredicate = (issue: Issue) => boolean;
type IssueFilter = IssueMatch | IssuePredicate | (IssueMatch | IssuePredicate)[];

Name	Type	Default value	Description
include	IssueFilter	undefined	If object, defines issue properties that should be matched. If function, acts as a predicate where issue is an argument.
exclude	IssueFilter	undefined	Same as include but issues that match this predicate will be excluded.

Expand example

Include issues from the src directory, exclude eslint issues from .spec.ts files:

module.exports = {
  // ...the webpack configuration
  plugins: [
    new ForkTsCheckerWebpackPlugin({
      issue: {
        include: [
          { file: '**/src/**/*' }
        ],
        exclude: [
          { origin: 'eslint', file: '**/*.spec.ts' }
        ]
      }
    })
  ]
};

Vue.js

⚠️ There are additional constraints regarding Vue.js Single File Component support: ⚠️

• It requires TypeScript >= 3.8.0 (it's a limitation of the transpileOnly mode from ts-loader)
• It doesn't work with the build mode (project references)

To enable Vue.js support, follow these steps:

Expand Vue.js set up instruction

1. Ensure you have all required packages installed: ```sh # with npm npm install --save vue vue-class-component npm install --save-dev vue-loader ts-loader css-loader vue-template-compiler

with yarn

yarn add vue vue-class-component yarn add --dev vue-loader ts-loader css-loader vue-template-compiler

2. Add `tsconfig.json` configuration:
```json
{
  "compilerOptions": {
    "experimentalDecorators": true,
    "jsx": "preserve",
    "target": "ES5",
    "lib": ["ES6", "DOM"],
    "baseUrl": ".",
    "paths": {
      "@/*": ["src/*"],
      "~/*": ["src/*"]
    },
    "sourceMap": true,
    "importsNotUsedAsValues": "preserve"
  },
  "include": [
    "src/**/*.ts",
    "src/**/*.vue"
  ],
  "exclude": [
    "node_modules"
  ]
}

1. Add webpack.config.js configuration: ```js const path = require('path'); const VueLoaderPlugin = require('vue-loader/lib/plugin'); const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');

module.exports = { entry: './src/index.ts', output: { filename: 'index.js', path: path.resolve(dirname, 'dist'), }, module: { rules: [ { test: /.vue$/, loader: 'vue-loader' }, { test: /.ts$/, loader: 'ts-loader', exclude: /node_modules/, options: { appendTsSuffixTo: [/.vue$/], transpileOnly: true } }, { test: /.css$/, loader: 'css-loader' }, ], }, resolve: { extensions: ['.ts', '.js', '.vue', '.json'], alias: { '@': path.resolve(dirname, './src'), '~': path.resolve(__dirname, './src'), } }, plugins: [ new VueLoaderPlugin(), new ForkTsCheckerWebpackPlugin({ typescript: { extensions: { vue: true } } }) ] };

4. Add `src/types/vue.d.ts` file to shim `.vue` modules:
```typescript
declare module "*.vue" {
  import Vue from "vue";
  export default Vue;
}

1. If you are working in VSCode, you can get the Vetur extension to complete the developer workflow.

Plugin hooks

This plugin provides some custom webpack hooks:

Hook key	Type	Params	Description
start	AsyncSeriesWaterfallHook	change, compilation	Starts issues checking for a compilation. It's an async waterfall hook, so you can modify the list of changed and removed files or delay the start of the service.
waiting	SyncHook	compilation	Waiting for the issues checking.
canceled	SyncHook	compilation	Issues checking for the compilation has been canceled.
error	SyncHook	compilation	An error occurred during issues checking.
issues	SyncWaterfallHook	issues, compilation	Issues have been received and will be reported. It's a waterfall hook, so you can modify the list of received issues.

To access plugin hooks and tap into the event, we need to use the getCompilerHooks static method. When we call this method with a webpack compiler instance, it returns the object with tapable hooks where you can pass in your callbacks.

// ./src/webpack/MyWebpackPlugin.js
const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');

class MyWebpackPlugin {
  apply(compiler) {
    const hooks = ForkTsCheckerWebpackPlugin.getCompilerHooks(compiler);

    // log some message on waiting
    hooks.waiting.tap('MyPlugin', () => {
      console.log('waiting for issues');
    });
    // don't show warnings
    hooks.issues.tap('MyPlugin', (issues) => 
      issues.filter((issue) => issue.severity === 'error')
    );
  }
}

module.exports = MyWebpackPlugin;

// webpack.config.js
const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');
const MyWebpackPlugin = require('./src/webpack/MyWebpackPlugin');

module.exports = {
  /* ... */
  plugins: [
    new ForkTsCheckerWebpackPlugin(),
    new MyWebpackPlugin()
  ]
};

Typings

To use the plugin typings, you have to install @types/webpack. It's not included by default to not collide with your existing typings (@types/webpack imports @types/node). It's an old TypeScript issue, the alternative is to set skipLibCheck: true in the compilerOptions 😉

# with npm
npm install --save-dev @types/webpack

# with yarn
yarn add --dev @types/webpack

Profiling types resolution

Starting from TypeScript 4.1.0, you can profile long type checks by setting "generateTrace" compiler option. This is an instruction from microsoft/TypeScript#40063:

1. Set "generateTrace": "{folderName}" in your tsconfig.json
2. Look in the resulting folder. If you used build mode, there will be a legend.json telling you what went where. Otherwise, there will be trace.json file and types.json files.
3. Navigate to edge://tracing or chrome://tracing and load trace.json
4. Expand Process 1 with the little triangle in the left sidebar
5. Click on different blocks to see their payloads in the bottom pane
6. Open types.json in an editor
7. When you see a type ID in the tracing output, go-to-line {id} to find data about that type

Related projects

• ts-loader - TypeScript loader for webpack.
• babel-loader - Alternative TypeScript loader for webpack.
• fork-ts-checker-notifier-webpack-plugin - Notifies about build status using system notifications (similar to the webpack-notifier).

Credits

This plugin was created in Realytics in 2017. Thank you for supporting Open Source.

License

MIT License