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.

# 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)

// 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 theexamples directory.

Modules resolution

It's very important to be aware that this plugin uses TypeScript's, notwebpack'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).

TypeScript options

Options for the TypeScript checker (typescript option object).

TypeScript extensions options

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

ESLint options

Options for the ESLint linter (eslint option object).

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)[];

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:

# 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

{
  "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"
  ]
}

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
        }
      }
    })
  ]
};

declare module "*.vue" {
  import Vue from "vue";
  export default Vue;
}

Plugin hooks

This plugin provides some custom webpack hooks:

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 withtapable 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 yourexisting 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 bysetting "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