privatenumber/esbuild-loader

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)!

[!TIP] Are you using TypeScript with Node.js?

Supercharge your Node.js with TypeScript support using tsx!

tsx is a simple, lightweight, and blazing fast alternative to ts-node.

→ Learn more about tsx

^{Already a sponsor? Join the discussion in the Development repo!}

🚀 Install

npm i -D esbuild-loader

🚦 Quick Setup

To leverage esbuild-loader in your Webpack configuration, add a new rule for esbuild-loader matching the files you want to transform, such as .js, .jsx, .ts, or .tsx. Make sure to remove any other loaders you were using before (e.g. babel-loader/ts-loader).

Here's an example of how to set it up in your webpack.config.js:

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

              // Other rules...
          ],
      },
  }

In this setup, esbuild will automatically determine how to handle each file based on its extension:

• .js files will be treated as JS (no JSX allowed)
• .jsx as JSX
• .ts as TS (no TSX allowed)
• .tsx as TSX

If you want to force a specific loader on different file extensions (e.g. to allow JSX in .js files), you can use the loader option:

 {
     test: /\.js$/,
     loader: 'esbuild-loader',
     options: {
+        // Treat `.js` files as `.jsx` files
+        loader: 'jsx',

         // JavaScript version to transpile to
         target: 'es2015'
     }
 }

Loader

JavaScript

esbuild-loader can be used in-place of babel-loader to transpile new JavaScript syntax into code compatible with older JavaScript engines.

While this ensures your code can run smoothly across various environments, note that it can bloat your output code (like Babel).

The default target is esnext, which means it doesn't perform any transpilations.

To specify a target JavaScript engine that only supports ES2015, use the following configuration in your webpack.config.js:

 {
     test: /\.jsx?$/,
     loader: 'esbuild-loader',
     options: {
+        target: 'es2015',
     },
 }

For a detailed list of supported transpilations and versions, refer to the esbuild documentation.

TypeScript

esbuild-loader can be used in-place of ts-loader to compile TypeScript.

({
    // `.ts` or `.tsx` files
    test: /\.tsx?$/,
    loader: 'esbuild-loader'
})

[!IMPORTANT] It's possible to use loader: 'tsx' for both .ts and .tsx files, but this could lead to unexpected behavior as TypeScript and TSX do not have compatible syntaxes.

→ Read more

tsconfig.json

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

If it's under a custom name, you can pass 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.

The tsconfigRaw option can be used to pass in a raw tsconfig object, but it will not resolve the extends property.

Caveats

• esbuild only supports a subset of tsconfig options (see TransformOptions interface).

• Enable isolatedModules to avoid mis-compilation with features like re-exporting types.

• Enable esModuleInterop to make TypeScript's type system compatible with ESM imports.

• Features that require type interpretation, such as emitDecoratorMetadata and declaration, are not supported.

→ Read more about TypeScript Caveats

tsconfig.json Paths

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

Since esbuild-loader only transforms code, it cannot aid Webpack with resolving paths.

Type-checking

esbuild does not type check your code. And 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

Defining constants

Use the define option to replace global identifiers with constant expressions:

 {
     test: /\.[jt]sx?$/,
     loader: 'esbuild-loader',
     options: {
+        define: {
+            'process.env.NODE_ENV': JSON.stringify('production'),
+        },
     },
 }

[!TIP] The loader's define works with all devtools, including eval-based ones. If you're using the plugin's define and it's not working, try the loader instead.

EsbuildPlugin

Minification

Esbuild supports JavaScript minification, offering a faster alternative to traditional JS minifiers like Terser or UglifyJs. Minification is crucial for reducing file size and improving load times in web development. For a comparative analysis of its performance, refer to these minification benchmarks.

In webpack.config.js:

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

  module.exports = {
      ...,

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

[!TIP] Utilizing the target option allows for the use of newer JavaScript syntax, enhancing minification effectiveness.

Defining constants

Webpack's DefinePlugin can replaced with EsbuildPlugin to define global constants. This could speed up the build by removing the parsing costs associated with the DefinePlugin.

In webpack.config.js:

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

  module.exports = {
      // ...,

      plugins:[
-         new DefinePlugin({
-             'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
-         })
+         new EsbuildPlugin({
+             define: {
+                 'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
+             },
+         }),
      ]
  }

[!WARNING] The plugin's define option does not work with eval-based devtools (e.g., eval, eval-source-map). This is because eval devtools wrap module code in eval() strings, and esbuild's define cannot replace identifiers inside string literals. If you need to use define with eval devtools, use the loader's define option instead, which transforms files before bundling.

Transpilation

If your project does not use TypeScript, JSX, or any other syntax that requires additional configuration beyond what Webpack provides, you can use EsbuildPlugin for transpilation instead of the loader.

It will be faster because there's fewer files to process, and will produce a smaller output because polyfills will only be added once for the entire build as opposed to per file.

To utilize esbuild for transpilation, simply set the target option on the plugin to specify which syntax support you want.

CSS Minification

Depending on your setup, there are two ways to minify CSS. You should already have CSS loading setup using css-loader.

CSS assets

If the CSS is extracted and emitted as .css 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 injected with JavaScript 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,
+                         },
+                     },
                  ],
              },
          ],
      },
  }

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).

[!WARNING]
⚠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,
                  },
              },
          ],
      },
  }

Setup examples

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

→ esbuild-loader examples

⚙️ 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.

define

Type: { [key: string]: string }

Replace global identifiers with constant expressions (e.g., 'process.env.NODE_ENV': JSON.stringify('production')).

[!TIP] Unlike the plugin's define option, the loader's define works with all devtools including eval-based ones (e.g., eval-source-map). This is because the loader transforms files before Webpack bundles them, so identifiers are replaced before any eval wrapping occurs.

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.

💡 Support

For personalized assistance, take advantage of my Priority Support service.

Whether it's about Webpack configuration, esbuild, or TypeScript, I'm here to guide you every step of the way!

🙋‍♀️ 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 a JS runtime 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.

💞 Related projects

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!

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