.fusionrc.js

Fusion supports a .fusionrc.js in the root directory of your application. This must be a CommonJS module exporting an object.

This configuration object supports the following fields:

babel

Adding plugins/presets

For example, to add your own Babel plugins/preset:

module.exports = {
  babel: {
    presets: ['some-babel-preset'],
    plugins: ['some-babel-plugin'],
  },
};

Import side effects, import pruning, and tree shaking

defaultImportSideEffects

This option controls how fusion-cli handles pruning of unused/unreachable import statements.

By default this is true. In other words, import statements to other packages are assumed to have import side effects unless specified otherwise. Therefore, any unreachable/unused import statements cannot be pruned/tree-shaken unless the module being imported is explicitly marked as sideEffects: false in its package.json. This is the most conservative setting.

Setting this to false means that unreachable/unused imports to packages into your app may be pruned (unless they explicitly specify import side effects in their package.json via the sideEffects field). Note that this only applies to imports to other packages from within your application source code. Imports within other packages to other packages will not be affected by this configuration. This is the recommended setting because it allows for a greater degree of import pruning with respect to imports used only in __BROWSER__ or __NODE__.

Note: defaultImportSideEffects applies to packages but not your application code. Use the standard sideEffects field in your app package.json to specify which project code files, when imported, cause side effects to happen.

module.exports = {
  // All packages omitting a sideEffects field are assumed to be free of import side effects
  defaultImportSideEffects: false,
};

Setting this to an array of package names is the same as false with the exception of the specified packages.

module.exports = {
  // All packages omitting a sideEffects field are assumed to be free of import side effects
  // *except* core-js, which is assumed to have import side effects.
  defaultImportSideEffects: ["core-js"],
};

Note: Fusion.js automatically excludes core-js, regenerator-runtime from this optimization.

assumeNoImportSideEffects

By default this is false.

Setting this to true enables the assumption that modules in your code do not have any import side effects. This assumption allows for more powerful tree shaking and pruning of unused imports.

This option may be useful if you import modules that use Node.js built-ins. This option makes it easier to avoid unintentionally including server-specific code in the browser bundle.

Setting this to an array of package names is the same as true with the exception of the specified packages.

module.exports = {
  // All packages omitting a sideEffects field are assumed to be free of import side effects
  // *except* core-js, which is assumed to have import side effects.
  assumeNoImportSideEffects: ["core-js"],
};

Note: Fusion.js automatically excludes core-js, regenerator-runtime from this optimization.

For specifics regarding implementation details, see:

• https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free
• https://github.com/webpack/webpack/tree/master/examples/side-effects
• https://stackoverflow.com/questions/49160752/what-does-webpack-4-expect-from-a-package-with-sideeffects-false/49203452#49203452

In the future, it is possible that some form of this behavior may be turned on by default (with ways to opt-out instead).

nodeBuiltins

This is an optional property that can be used to override the Fusion.js defaults for https://v4.webpack.js.org/configuration/node/ in the browser bundle.

module.exports = {
  nodeBuiltins: {
    Buffer: true,
  },
};

gzip

This is an optional property that can be used to override the Fusion.js defaults for compressing projects using zlib in production builds. If left undefined, this property will default to true.

module.exports = {
  gzip: false,
};

brotli

This is an optional property that can be used to override the Fusion.js defaults for compressing projects using brotli in production builds. If left undefined, this property will default to true.

module.exports = {
  brotli: false,
};

onBuildEnd

This is an optional property that can be used to invoke a callback function when a build is completed. The function is passed metadata about the build including the build time, build target, and other build options.

module.exports = {
  onBuildEnd: function (stats) {
    console.log(stats.buildTime);
  }
};

disableBuildCache

This is an optional property that can be used to override the Fusion.js defaults for enabling persistent build cache. If left undefined, this property will default to false.

module.exports = {
  disableBuildCache: true,
};

experimentalEsbuildMinifier

This is an optional property that can be used to configure Fusion.js to use experimental esbuild minifier instead of Terser. If left undefined, this property will default to false.

module.exports = {
  experimentalEsbuildMinifier: true,
};