ts-loader

What is ts-loader?

The ts-loader package is a TypeScript loader for webpack that allows you to transpile TypeScript files (.ts, .tsx) to JavaScript while bundling with webpack. It enables you to integrate TypeScript into your webpack build process.

What are ts-loader's main functionalities?

Transpilation of TypeScript to JavaScript

This feature allows you to compile TypeScript files into JavaScript, enabling you to use TypeScript in your webpack projects. The code sample shows a webpack configuration that uses ts-loader to process files with .ts or .tsx extensions.

module.exports = {
  mode: 'development',
  entry: './src/index.ts',
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/
      }
    ]
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js']
  },
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

Integration with webpack's watch mode

ts-loader works seamlessly with webpack's watch mode, which recompiles your code when changes are detected. This feature is useful for development as it provides a fast feedback loop.

webpack --watch

Source map support

ts-loader supports the generation of source maps, which help in debugging by mapping the compiled code back to the original TypeScript source code. The code sample shows how to enable inline source maps in your webpack configuration.

module.exports = {
  devtool: 'inline-source-map',
  // ... other webpack configuration
};

Other packages similar to ts-loader

awesome-typescript-loader

Similar to ts-loader, awesome-typescript-loader is another TypeScript loader for webpack. It offers features like Babel integration and type checking in a separate process. However, it is no longer actively maintained, and users are recommended to switch to ts-loader or other alternatives.

babel-loader

While not a TypeScript-specific loader, babel-loader can be used in conjunction with @babel/preset-typescript to transpile TypeScript code. It is part of the Babel ecosystem and is often used for its broader transformation capabilities and plugin ecosystem.

esbuild-loader

esbuild-loader uses the esbuild bundler to transpile TypeScript (and other files) at a much faster rate than traditional loaders. It is known for its speed and efficiency, making it a strong alternative to ts-loader, especially in large projects where build time is a concern.

README

TypeScript loader for webpack

This is the typescript loader for webpack.

Getting Started

Examples

We have a number of example setups to accomodate different workflows. From "vanilla" ts-loader, to using ts-loader in combination with babel for transpilation, happypack or thread-loader for faster builds and fork-ts-checker-webpack-plugin for performing type checking in a separate process. Our examples can be found here.

Babel

ts-loader works very well in combination with babel and babel-loader. There is an example of this in the official TypeScript Samples. Alternatively take a look at our own example.

Faster Builds

As your project becomes bigger and bigger, compilation time increases linearly. It's because typescript's semantic checker has to inspect all files on every rebuild. The simple solution is to disable it by using the transpileOnly: true option, but doing so leaves you without type checking.

You probably don't want to give up type checking; that's rather the point of TypeScript. So what you can do is use the fork-ts-checker-webpack-plugin. It runs the type checker on a separate process, so your build remains fast thanks to transpileOnly: true but you still have the type checking. Also, the plugin has several optimizations to make incremental type checking faster (AST cache, multiple workers).

If you'd like to see a simple setup take a look at our simple example. For a more complex setup take a look at our more involved example.

If you'd like to make things even faster still (I know, right?) then you might want to consider using ts-loader with happypack which speeds builds by parallelising work. (This should be used in combination with fork-ts-checker-webpack-plugin for typechecking.) If you'd like to see a simple setup take a look at our simple example. For a more complex setup take a look at our more involved example.

There is a "webpack-way" of parallelising builds. Instead of using happypack you can use ts-loader with ts-loader with thread-loader and cache-loader in combination. (Again, this should be used in combination with fork-ts-checker-webpack-plugin for typechecking.) If you'd like to see a simple setup take a look at our simple example. For a more complex setup take a look at our more involved example.

Installation

npm install ts-loader

You will also need to install TypeScript if you have not already.

npm install typescript

Running

Use webpack like normal, including webpack --watch and webpack-dev-server, or through another build system using the Node.js API.

Configuration

1. Create or update webpack.config.js like so:

   module.exports = {
     devtool: 'inline-source-map',
     entry: './app.ts',
     output: {
       filename: 'bundle.js'
     },
     resolve: {
       // Add `.ts` and `.tsx` as a resolvable extension.
       extensions: ['.ts', '.tsx', '.js'] // note if using webpack 1 you'd also need a '' in the array as well
     },
     module: {
       loaders: [ // loaders will work with webpack 1 or 2; but will be renamed "rules" in future
         // all files with a `.ts` or `.tsx` extension will be handled by `ts-loader`
         { test: /\.tsx?$/, loader: 'ts-loader' }
       ]
     }
   }
   

2. Add a tsconfig.json file. (The one below is super simple; but you can tweak this to your hearts desire)

   {
     "compilerOptions": {
       "sourceMap": true
     }
   }
   

The tsconfig.json file controls TypeScript-related options so that your IDE, the tsc command, and this loader all share the same options.

devtool / sourcemaps

If you want to be able to debug your original source then you can thanks to the magic of sourcemaps. There are 2 steps to getting this set up with ts-loader and webpack.

First, for ts-loader to produce sourcemaps, you will need to set the tsconfig.json option as "sourceMap": true.

Second, you need to set the devtool option in your webpack.config.js to support the type of sourcemaps you want. To make your choice have a read of the devtool webpack docs. You may be somewhat daunted by the choice available. You may also want to vary the sourcemap strategy depending on your build environment. Here are some example strategies for different environments:

• devtool: 'inline-source-map' - Solid sourcemap support; the best "all-rounder". Works well with karma-webpack (not all strategies do)
• devtool: 'cheap-module-eval-source-map' - Best support for sourcemaps whilst debugging.
• devtool: 'source-map' - Approach that plays well with UglifyJsPlugin; typically you might use this in Production

Code Splitting and Loading Other Resources

Loading css and other resources is possible but you will need to make sure that you have defined the require function in a declaration file.

declare var require: {
    <T>(path: string): T;
    (paths: string[], callback: (...modules: any[]) => void): void;
    ensure: (paths: string[], callback: (require: <T>(path: string) => T) => void) => void;
};

Then you can simply require assets or chunks per the webpack documentation.

require('!style!css!./style.css');

The same basic process is required for code splitting. In this case, you import modules you need but you don't directly use them. Instead you require them at split points. See this example and this example for more details.

TypeScript 2.4 provides support for ECMAScript's new import() calls. These calls import a module and return a promise to that module. This is also supported in webpack - details on usage can be found here. Happy code splitting!

Declarations (.d.ts)

To output a built .d.ts file, you can set "declaration": true in your tsconfig, and use the DeclarationBundlerPlugin in your webpack config.

Compatibility

TypeScript / Webpack

ts-loader supports the latest and greatest version of TypeScript right back to v1.6.

ts-loader supports webpack 2. It may well still work with webpack 1 but it does not officially support webpack 1 any longer. Our continuous integration test suites run against webpack 2; not webpack 1.

A full test suite runs each night (and on each pull request). It runs both on Linux and Windows, testing ts-loader against major releases of TypeScript. The test suite also runs against TypeScript@next (because we want to use it as much as you do).

If you become aware of issues not caught by the test suite then please let us know. Better yet, write a test and submit it in a PR!

Failing the build on TypeScript compilation error

The build should fail on TypeScript compilation errors as of webpack 2. If for some reason it does not, you can use the webpack-fail-plugin.

For more background have a read of this issue.

Options

There are two types of options: TypeScript options (aka "compiler options") and loader options. TypeScript options should be set using a tsconfig.json file. Loader options can be set either using a query when specifying the loader or through the options property in the webpack configuration:

module.exports = {
  ...
  module: {
    rules: [
      { 
        test: /\.tsx?$/, 
        loader: 'ts-loader', 
        options: {
          transpileOnly: true
        } 
      }
    ]
  }
}

Alternatively this can be configured using a query:

module.exports = {
  ...
  module: {
    loaders: [
      // specify option using query
      { 
        test: /\.tsx?$/,
        loader: 'ts-loader?' + JSON.stringify({
          transpileOnly: true
        }) }
    ]
  }
}

For a full breakdown of the power of query syntax have a read of this.

Loader Options

transpileOnly (boolean) (default=false)

If you want to speed up compilation significantly you can set this flag. However, many of the benefits you get from static type checking between different dependencies in your application will be lost.

It's advisable to use transpileOnly alongside the fork-ts-checker-webpack-plugin to get full type checking again. To see what this looks like in practice then either take a look at our simple example. For a more complex setup take a look at our more involved example.

happyPackMode (boolean) (default=false)

If you're using HappyPack or thread-loader to parallise your builds then you'll need to set this to true. This implicitly sets *transpileOnly* to true and WARNING! stops registering all errors to webpack.

It's advisable to use this with the fork-ts-checker-webpack-plugin to get full type checking again. To see what this looks like in practice then either take a look at our simple HappyPack example / our simple thread-loader example. For a more complex setup take a look at our more involved HappyPack example / more involved thread-loader example. IMPORTANT: If you are using fork-ts-checker-webpack-plugin alongside HappyPack or thread-loader then ensure you set the checkSyntacticErrors option like so:

        new ForkTsCheckerWebpackPlugin({ checkSyntacticErrors: true })

This will ensure that the plugin checks for both syntactic errors (eg const array = [{} {}];) and semantic errors (eg const x: number = '1';). By default the plugin only checks for semantic errors (as when used with ts-loader in transpileOnly mode, ts-loader will still report syntactic errors).

getCustomTransformers ( () => { before?: TransformerFactory[]; after?: TransformerFactory[]; } )

Provide custom transformers - only compatible with TypeScript 2.3+ (and 2.4 if using transpileOnly mode). For example usage take a look at typescript-plugin-styled-components or our test.

logInfoToStdOut (boolean) (default=false)

This is important if you read from stdout or stderr and for proper error handling. The default value ensures that you can read from stdout e.g. via pipes or you use webpack -j to generate json output.

logLevel (string) (default=info)

Can be info, warn or error which limits the log output to the specified log level. Beware of the fact that errors are written to stderr and everything else is written to stderr (or stdout if logInfoToStdOut is true).

silent (boolean) (default=false)

If true, no console.log messages will be emitted. Note that most error messages are emitted via webpack which is not affected by this flag.

ignoreDiagnostics (number[]) (default=[])

You can squelch certain TypeScript errors by specifying an array of diagnostic codes to ignore.

compiler (string) (default='typescript')

Allows use of TypeScript compilers other than the official one. Should be set to the NPM name of the compiler, eg ntypescript.

configFileName (string) (default='tsconfig.json')

This option has been deprecated in favor of configFile.

configFile (string) (default='tsconfig.json')

Allows you to specify where to find the TypeScript configuration file.

You may provide

• just a file name. The loader then will search for the config file of each entry point in the respective entry point's containing folder. If a config file cannot be found there, it will travel up the parent directory chain and look for the config file in those folders.
• a relative path to the configuration file. It will be resolved relative to the respective .ts entry file.
• an absolute path to the configuration file.

visualStudioErrorFormat (boolean) (default=false)

If true, the TypeScript compiler output for an error or a warning, e.g. (3,14): error TS4711: you did something very wrong, in file myFile will instead be myFile(3,14): error TS4711: you did something very wrong (notice the file name at the beginning). This way Visual Studio will interpret this line and show any errors or warnings in the error list. This enables navigation to the file/line/column through double click.

compilerOptions (object) (default={})

Allows overriding TypeScript options. Should be specified in the same format as you would do for the compilerOptions property in tsconfig.json.

instance (string)

Advanced option to force files to go through different instances of the TypeScript compiler. Can be used to force segregation between different parts of your code.

entryFileIsJs (boolean) (default=false)

To be used in concert with the allowJs compiler option. If your entry file is JS then you'll need to set this option to true. Please note that this is rather unusual and will generally not be necessary when using allowJs.

appendTsSuffixTo (RegExp[]) (default=[])

appendTsxSuffixTo (RegExp[]) (default=[])

A list of regular expressions to be matched against filename. If filename matches one of the regular expressions, a .ts or .tsx suffix will be appended to that filename.

This is useful for *.vue file format for now. (Probably will benefit from the new single file format in the future.)

Example:

webpack.config.js:

module.exports = {
    entry: './index.vue',
    output: { filename: 'bundle.js' },
    resolve: {
        extensions: ['.ts', '.vue']
    },
    module: {
        rules: [
            { test: /\.vue$/, loader: 'vue-loader' },
            { test: /\.ts$/, loader: 'ts-loader', options: { appendTsSuffixTo: [/\.vue$/] } }
        ]
    } 
}

index.vue

<template><p>hello {{msg}}</p></template>
<script lang="ts">
export default {
  data(): Object {
    return {
      msg: "world"
    }
  },
}
</script>

We can handle .tsx by quite similar way:

webpack.config.js:

module.exports = {
    entry: './index.vue',
    output: { filename: 'bundle.js' },
    resolve: {
        extensions: ['.ts', '.tsx', '.vue', '.vuex']
    },
    module: {
        rules: [
            { test: /\.vue$/, loader: 'vue-loader',
              options: {
                loaders: {
                  ts: 'ts-loader',
                  tsx: 'babel-loader!ts-loader',
                }
              }
            },
            { test: /\.ts$/, loader: 'ts-loader', options: { appendTsSuffixTo: [/TS\.vue$/] } }
            { test: /\.tsx$/, loader: 'babel-loader!ts-loader', options: { appendTsxSuffixTo: [/TSX\.vue$/] } }
        ]
    } 
}

tsconfig.json (set jsx option to preserve to let babel handle jsx)

{
  "compilerOptions": {
    "jsx": "preserve"
  }
}

index.vue

<script lang="tsx">
export default {
  functional: true,
  render(h, c) {
    return (<div>Content</div>);
  }
}
</script>

Or if you want to use only tsx, just use the appendTsxSuffixTo option only:

            { test: /\.ts$/, loader: 'ts-loader' }
            { test: /\.tsx$/, loader: 'babel-loader!ts-loader', options: { appendTsxSuffixTo: [/\.vue$/] } }

LoaderOptionsPlugin

There's a known "gotcha" if you are using webpack 2 with the LoaderOptionsPlugin. If you are faced with the Cannot read property 'unsafeCache' of undefined error then you probably need to supply a resolve object as below: (Thanks @jeffijoe!)

new LoaderOptionsPlugin({		
  debug: false,		
  options: {		
    resolve: {
      extensions: ['.ts', '.tsx', '.js']
    }	
  }		
})		

It's worth noting that use of the LoaderOptionsPlugin is only supposed to be a stopgap measure. You may want to look at removing it entirely.

Contributing

This is your TypeScript loader! We want you to help make it even better. Please feel free to contribute; see the contributor's guide to get started.

License

MIT License