esbuild-loader

What is esbuild-loader?

esbuild-loader is a Webpack loader that leverages the esbuild bundler to perform fast JavaScript and TypeScript transpilation and bundling. It is designed to significantly speed up the build process by using esbuild's highly optimized and parallelized architecture.

What are esbuild-loader's main functionalities?

JavaScript and TypeScript Transpilation

This feature allows you to transpile JavaScript and TypeScript files using esbuild. The code sample demonstrates how to configure esbuild-loader in a Webpack configuration to handle `.tsx` and `.ts` files, targeting ES2015 syntax.

module.exports = {
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        loader: 'esbuild-loader',
        options: {
          loader: 'tsx', // Or 'ts' if you don't need tsx
          target: 'es2015' // Syntax to compile to (see options below for possible values)
        }
      }
    ]
  }
};

Minification

esbuild-loader can also be used to minify JavaScript code. The code sample shows how to use the `EsbuildPlugin` to enable minification in a Webpack configuration, targeting ES2015 syntax.

const EsbuildPlugin = require('esbuild-loader').EsbuildPlugin;

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new EsbuildPlugin({
        target: 'es2015' // Syntax to compile to (see options below for possible values)
      })
    ]
  }
};

CSS Loading

esbuild-loader can also handle CSS files. The code sample demonstrates how to configure esbuild-loader to load and minify CSS files in a Webpack configuration.

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-loader',
          {
            loader: 'esbuild-loader',
            options: {
              loader: 'css',
              minify: true
            }
          }
        ]
      }
    ]
  }
};

Other packages similar to esbuild-loader

babel-loader

babel-loader is a Webpack loader that uses Babel to transpile JavaScript and TypeScript files. While babel-loader is highly configurable and supports a wide range of plugins and presets, it is generally slower than esbuild-loader due to Babel's single-threaded architecture.

ts-loader

ts-loader is a Webpack loader specifically designed for TypeScript transpilation using the TypeScript compiler (tsc). It provides fine-grained control over TypeScript compilation but is slower compared to esbuild-loader, which uses esbuild's faster, parallelized architecture.

terser-webpack-plugin

terser-webpack-plugin is a Webpack plugin used for minifying JavaScript files using Terser. While it is highly configurable and widely used, it is generally slower than esbuild-loader's minification capabilities, which leverage esbuild's optimized performance.

README

esbuild-loader

Speed up your Webpack build with esbuild! 🔥

esbuild is a JavaScript bundler written in Go that supports blazing fast ESNext & TypeScript transpilation and JS minification.

esbuild-loader lets you harness the speed of esbuild in your Webpack build by offering faster alternatives for transpilation (eg. babel-loader/ts-loader) and minification (eg. Terser)!

Curious how much faster your build will be? See what users are saying.

---

🤫 Psst! Want to power up your Node.js with esbuild?

Checkout our new project tsx, an esbuild enhanced Node.js runtime that can run TypeScript instantly!

---

_{Support this project by ⭐️ starring and sharing it. Follow me to see what other cool projects I'm working on! ❤️}

🚀 Install

npm i -D esbuild-loader

🚦 Quick Setup

Use esbuild-loader to transform new JavaScript syntax to support older browsers, and TypeScript to JavaScript

In your Webpack configuration, add a new rule for esbuild-loader matching the files you want to transform (e.g. .js, .jsx, .ts, .tsx).

If you were using other loaders before (e.g. babel-loader/ts-loader), make sure to remove them.

webpack.config.js:

  module.exports = {
    module: {
      rules: [
-       {
-         test: /\.js$/,
-         use: 'babel-loader'
-       },
-       {
-         test: /\.tsx?$/,
-         use: 'ts-loader'
-       },
+       {
+         // Match js, jsx, ts & tsx files
+         test: /\.[jt]sx?$/,
+         loader: 'esbuild-loader',
+         options: {
+           // JavaScript version to compile to
+           target: 'es2015'
+         }
+       },

        ...
      ],
    },
  }

TypeScript

tsconfig.json

If you have a tsconfig.json file in your project, esbuild-loader will automatically load it.

If you use a custom name, you can pass it in the path via tsconfig option:

  {
     test: /\.tsx?$/,
     loader: 'esbuild-loader',
     options: {
+      tsconfig: './tsconfig.custom.json'
     }
  }

Behind the scenes, get-tsconfig is used to load the tsconfig, and to also resolve the extends property if it exists.

You can also use the tsconfigRaw option to pass in a raw tsconfig object, but it will not resolve the extends property.

⚠️ esbuild only supports a subset of tsconfig options (see TransformOptions interface) and does not do type-checks. It's recommended to use a type-aware IDE or tsc --noEmit for type-checking instead. It is also recommended to enable isolatedModules and esModuleInterop options in your tsconfig by the esbuild docs.

tsconfig.json Paths

Use tsconfig-paths-webpack-plugin to add support for tsconfig.json#paths.

Since esbuild-loader only uses esbuild to transform code, it cannot help Webpack with resolving paths.

Minification

You can replace JS minifiers like Terser or UglifyJs. Checkout the benchmarks to see how much faster esbuild is. The target option tells esbuild that it can use newer JS syntax to perform better minification.

In webpack.config.js:

+ const { EsbuildPlugin } = require('esbuild-loader')

  module.exports = {
    ...,

+   optimization: {
+     minimizer: [
+       new EsbuildPlugin({
+         target: 'es2015'  // Syntax to compile to (see options below for possible values)
+       })
+     ]
+   },
  }

💁‍♀️ Protip: Use the plugin in-place of the loader to transpile the JS

If you're not using TypeScript, JSX, or any syntax unsupported by Webpack, you can also leverage the minifier for transpilation (as an alternative to Babel). It will be faster because there's less files to work on and will produce a smaller output because the polyfills will only be bundled once for the entire build instead of per file. Simply set the target option on the minifier to specify which support level you want.

CSS Minification

There are two ways to minify CSS, depending on your setup. You should already have CSS setup in your build using css-loader.

CSS assets

If the CSS is extracted and emitted as a separate file, you can replace CSS minification plugins like css-minimizer-webpack-plugin with the EsbuildPlugin.

Assuming the CSS is extracted using something like MiniCssExtractPlugin, in webpack.config.js:

  const { EsbuildPlugin } = require('esbuild-loader')
  const MiniCssExtractPlugin = require('mini-css-extract-plugin');

  module.exports = {
    ...,

    optimization: {
      minimizer: [
        new EsbuildPlugin({
          target: 'es2015',
+         css: true  // Apply minification to CSS assets
        })
      ]
    },

    module: {
      rules: [
        {
          test: /\.css$/i,
          use: [
            MiniCssExtractPlugin.loader,
            'css-loader'
          ]
        }
      ]
    },

    plugins: [
      new MiniCssExtractPlugin()
    ]
  }

CSS in JS

If your CSS is not emitted as a CSS file, but rather loaded via JS using something like style-loader, you can use the loader for minification.

In webpack.config.js:

  module.exports = {
    ...,

    module: {
      rules: [
        {
          test: /\.css$/i,
          use: [
            'style-loader',
            'css-loader',
+           {
+             loader: 'esbuild-loader',
+             options: {
+               minify: true
+             }
+           }
          ]
        }
      ]
    }
  }

Examples

If you'd like to see working Webpack builds that use esbuild-loader for basic JS, React, TypeScript, or Next.js, check out the examples repo.

Bring your own esbuild (Advanced)

esbuild-loader comes with a version of esbuild it has been tested to work with. However, esbuild has a frequent release cadence, and while we try to keep up with the important releases, it can get outdated.

To work around this, you can use the implementation option in the loader or the plugin to pass in your own version of esbuild (eg. a newer one).

⚠️ esbuild is not stable yet and can have dramatic differences across releases. Using a different version of esbuild is not guaranteed to work.

+ const esbuild = require('esbuild')

  ...

  module.exports = {
    ...,

    module: {
      rules: [
        {
          test: ...,
          loader: 'esbuild-loader',
          options: {
            ...,
+           implementation: esbuild
          }
        }
      ]
    }
  }

The implementation option will be removed once esbuild reaches a stable release. Instead esbuild will become a peerDependency so you always provide your own.

⚙️ Options

Loader

The loader supports all Transform options from esbuild.

Note:

• Source-maps are automatically configured for you via devtool. sourcemap/sourcefile options are ignored.
• The root tsconfig.json is automatically detected for you. You don't need to pass in tsconfigRaw unless it's in a different path.

Here are some common configurations and custom options:

tsconfig

Type: string

Pass in the file path to a custom tsconfig file. If the file name is tsconfig.json, it will automatically detect it.

target

Type: string | Array<string>

Default: 'es2015'

The target environment (e.g. es2016, chrome80, esnext).

Read more about it in the esbuild docs.

loader

Type: 'js' | 'jsx' | 'ts' | 'tsx' | 'css' | 'json' | 'text' | 'base64' | 'file' | 'dataurl' | 'binary' | 'default'

Default: 'default'

The loader to use to handle the file. See the type for possible values.

By default, it automatically detects the loader based on the file extension.

Read more about it in the esbuild docs.

jsxFactory

Type: string

Default: React.createElement

Customize the JSX factory function name to use.

Read more about it in the esbuild docs.

jsxFragment

Type: string

Default: React.Fragment

Customize the JSX fragment function name to use.

Read more about it in the esbuild docs.

implementation

Type: { transform: Function }

Custom esbuild-loader option.

Use it to pass in a different esbuild version.

EsbuildPlugin

The loader supports all Transform options from esbuild.

target

Type: string | Array<string>

Default: 'esnext'

Target environment (e.g. 'es2016', ['chrome80', 'esnext'])

Read more about it in the esbuild docs.

Here are some common configurations and custom options:

format

Type: 'iife' | 'cjs' | 'esm'

Default:

• iife if both of these conditions are met:
  • Webpack's target is set to web
  • esbuild's target is not esnext
• undefined (no format conversion) otherwise

The default is iife when esbuild is configured to support a low target, because esbuild injects helper functions at the top of the code. On the web, having functions declared at the top of a script can pollute the global scope. In some cases, this can lead to a variable collision error. By setting format: 'iife', esbuild wraps the helper functions in an IIFE to prevent them from polluting the global.

Read more about it in the esbuild docs.

minify

Type: boolean

Default: true

Enable JS minification. Enables all minify* flags below.

To have nuanced control over minification, disable this and enable the specific minification you want below.

Read more about it in the esbuild docs.

minifyWhitespace

Type: boolean

Minify JS by removing whitespace.

minifyIdentifiers

Type: boolean

Minify JS by shortening identifiers.

minifySyntax

Type: boolean

Minify JS using equivalent but shorter syntax.

legalComments

Type: 'none' | 'inline' | 'eof' | 'external'

Default: 'inline'

Read more about it in the esbuild docs.

css

Type: boolean

Default: false

Whether to minify CSS files.

include

Type: string | RegExp | Array<string | RegExp>

To only apply the plugin to certain assets, pass in filters include

exclude

Type: string | RegExp | Array<string | RegExp>

To prevent the plugin from applying to certain assets, pass in filters to exclude

implementation

Type: { transform: Function }

Use it to pass in a different esbuild version.

🙋‍♀️ FAQ

Is it possible to use esbuild plugins?

No. esbuild plugins are only available in the build API. And esbuild-loader uses the transform API instead of the build API for two reasons:

1. The build API is for creating JS bundles, which is what Webpack does. If you want to use esbuild's build API, consider using esbuild directly instead of Webpack.

2. The build API reads directly from the file-system, but Webpack loaders operate in-memory. Webpack loaders are essentially just functions that are called with the source-code as the input. Not reading from the file-system allows loaders to be chainable. For example, using vue-loader to compile Single File Components (.vue files), then using esbuild-loader to transpile just the JS part of the SFC.

Is it possible to use esbuild's inject option?

No. The inject option is only available in the build API. And esbuild-loader uses the transform API.

However, you can use the Webpack equivalent ProvidePlugin instead.

If you're using React, check out this example on how to auto-import React in your components.

Is it possible to use Babel plugins?

No. If you really need them, consider porting them over to a Webpack loader.

And please don't chain babel-loader and esbuild-loader. The speed gains come from replacing babel-loader.

Why am I not getting a 100x speed improvement as advertised?

Running esbuild as a standalone bundler vs esbuild-loader + Webpack are completely different:

• esbuild is highly optimized, written in Go, and compiled to native code. Read more about it here.
• esbuild-loader is handled by Webpack in a JS runtime, which applies esbuild transforms per file. On top of that, there's likely other loaders & plugins in a Webpack config that slow it down.

Using any JS bundler introduces a bottleneck that makes reaching those speeds impossible. However, esbuild-loader can still speed up your build by removing the bottlenecks created by babel-loader, ts-loader, Terser, etc.

Will there be type-checking support?

According to the esbuild FAQ, it will not be supported.

Consider these type-checking alternatives:

• Using an IDEs like VSCode or WebStorm that has live type-checking built in
• Running tsc --noEmit to type check
• Integrating type-checking to your Webpack build as a separate process using fork-ts-checker-webpack-plugin

💞 Related

tsx

Node.js enhanced with esbuild to run TypeScript and ESM.

instant-mocha

Webpack-integrated Mocha test-runner with Webpack 5 support.

webpack-localize-assets-plugin

Localize/i18nalize your Webpack build. Optimized for multiple locales!