docs(commonjs): improve documentation and update types

Author: lukastaegert

packages/commonjs/README.md

@@ -76,21 +76,21 @@ commonjs({
 Type: `string | string[]`<br>
 Default: `null`
 
-A [minimatch pattern](https://github.com/isaacs/minimatch), or array of patterns, which specifies the files in the build the plugin should _ignore_. By default non-CommonJS modules are ignored.
+A [minimatch pattern](https://github.com/isaacs/minimatch), or array of patterns, which specifies the files in the build the plugin should _ignore_. By default, all files with extensions other than those in `extensions` or `".cjs"` are ignored, but you can exclude additional files. See also the `include` option.
 
 ### `include`
 
 Type: `string | string[]`<br>
 Default: `null`
 
-A [minimatch pattern](https://github.com/isaacs/minimatch), or array of patterns, which specifies the files in the build the plugin should operate on. By default CommonJS modules are targeted.
+A [minimatch pattern](https://github.com/isaacs/minimatch), or array of patterns, which specifies the files in the build the plugin should operate on. By default, all files with extension `".cjs"` or those in `extensions` are included, but you can narrow this list by only including specific files. These files will be analyzed and transpiled if either the analysis does not find ES module specific statements or `transformMixedEsModules` is `true`.
 
 ### `extensions`
 
 Type: `string[]`<br>
 Default: `['.js']`
 
-Search for extensions other than .js in the order specified.
+For extensionless imports, search for extensions other than .js in the order specified. Note that you need to make sure that non-JavaScript files are transpiled by another plugin first.
 
 ### `ignoreGlobal`
 
@@ -104,28 +104,28 @@ If true, uses of `global` won't be dealt with by this plugin.
 Type: `boolean`<br>
 Default: `true`
 
-If false, skips source map generation for CommonJS modules.
+If false, skips source map generation for CommonJS modules. This will improve performance.
 
 ### `transformMixedEsModules`
 
 Type: `boolean`<br>
 Default: `false`
 
-Instructs the plugin whether or not to enable mixed module transformations. This is useful in scenarios with mixed ES and CommonJS modules. Set to `true` if it's known that `require` calls should be transformed, or `false` if the code contains env detection and the `require` should survive a transformation.
+Instructs the plugin whether to enable mixed module transformations. This is useful in scenarios with modules that contain a mix of ES `import` statements and CommonJS `require` expressions. Set to `true` if `require` calls should be transformed to imports in mixed modules, or `false` if the `require` expressions should survive the transformation. The latter can be important if the code contains environment detection, or you are coding for an environment with special treatment for `require` calls such as [ElectronJS](https://www.electronjs.org/). See also the "ignore" option.
 
 ### `ignore`
 
 Type: `string[] | ((id: string) => boolean)`<br>
 Default: `[]`
 
-Sometimes you have to leave require statements unconverted. Pass an array containing the IDs or an `id => boolean` function. Only use this option if you know what you're doing!
+Sometimes you have to leave require statements unconverted. Pass an array containing the IDs or an `id => boolean` function.
 
 ### `esmExternals`
 
-Type: `boolean | string[] || ((id: string) => boolean)`
+Type: `boolean | string[] | ((id: string) => boolean)`
 Default: `false`
 
-Controls how imports from external dependencies are rendered. By default, all external dependencies are assumed to be CommonJS. This means they are rendered as default imports to be compatible with e.g. NodeJS where ES modules can only import a default export from a CommonJS dependency:
+Controls how to render imports from external dependencies. By default, this plugin assumes that all external dependencies are CommonJS. This means they are rendered as default imports to be compatible with e.g. NodeJS where ES modules can only import a default export from a CommonJS dependency:
 
 ```js
 // input
@@ -137,16 +137,16 @@ import foo from 'foo';
 
 This is likely not desired for ES module dependencies: Here `require` should usually return the namespace to be compatible with how bundled modules are handled.
 
-If you set `esmExternals` to `true`, all external dependencies are assumed to be ES modules and will adhere to the `requireReturnsDefault` option. If that option is not set, they will be rendered as namespace imports.
+If you set `esmExternals` to `true`, this plugins assumes that all external dependencies are ES modules and will adhere to the `requireReturnsDefault` option. If that option is not set, they will be rendered as namespace imports.
 
-You can also supply an array of ids that are to be treated as ES modules, or a function that will be passed each external id to determine if it is an ES module.
+You can also supply an array of ids to be treated as ES modules, or a function that will be passed each external id to determine if it is an ES module.
 
 ### `requireReturnsDefault`
 
 Type: `boolean | "auto" | "preferred" | ((id: string) => boolean | "auto" | "preferred")`<br>
 Default: `false`
 
-Controls what is returned when requiring an ES module or external dependency from a CommonJS file. By default, this plugin will render it as a namespace import, i.e.
+Controls what is returned when requiring an ES module from a CommonJS file. When using the `esmExternals` option, this will also apply to external modules. By default, this plugin will render those imports as namespace imports, i.e.
 
 ```js
 // input

packages/commonjs/test/types.ts

@@ -9,9 +9,11 @@ const config: import('rollup').RollupOptions = {
   plugins: [
     commonjs({
       include: 'node_modules/**',
+      esmExternals: ['foo', 'bar'],
       exclude: ['node_modules/foo/**', 'node_modules/bar/**', /node_modules/],
       extensions: ['.js', '.coffee'],
       ignoreGlobal: false,
+      requireReturnsDefault: 'auto',
       sourceMap: false,
       transformMixedEsModules: false,
       ignore: ['conditional-runtime-dependency'],

packages/commonjs/types/index.d.ts

@@ -1,58 +1,130 @@
 import { FilterPattern } from '@rollup/pluginutils';
 import { Plugin } from 'rollup';
 
+type RequireReturnsDefaultOption = boolean | 'auto' | 'preferred';
+
 interface RollupCommonJSOptions {
   /**
-   * non-CommonJS modules will be ignored, but you can also
-   * specifically include/exclude files
+   * A minimatch pattern, or array of patterns, which specifies the files in
+   * the build the plugin should operate on. By default, all files with
+   * extension `".cjs"` or those in `extensions` are included, but you can narrow
+   * this list by only including specific files. These files will be analyzed
+   * and transpiled if either the analysis does not find ES module specific
+   * statements or `transformMixedEsModules` is `true`.
    * @default undefined
    */
   include?: FilterPattern;
   /**
-   * non-CommonJS modules will be ignored, but you can also
-   * specifically include/exclude files
+   * A minimatch pattern, or array of patterns, which specifies the files in
+   * the build the plugin should _ignore_. By default, all files with
+   * extensions other than those in `extensions` or `".cjs"` are ignored, but you
+   * can exclude additional files. See also the `include` option.
    * @default undefined
    */
   exclude?: FilterPattern;
   /**
-   * search for files other than .js files (must already
-   * be transpiled by a previous plugin!)
+   * For extensionless imports, search for extensions other than .js in the
+   * order specified. Note that you need to make sure that non-JavaScript files
+   * are transpiled by another plugin first.
    * @default [ '.js' ]
    */
-  extensions?: ReadonlyArray<string | RegExp>;
+  extensions?: ReadonlyArray<string>;
   /**
-   * if true then uses of `global` won't be dealt with by this plugin
+   * If true then uses of `global` won't be dealt with by this plugin
    * @default false
    */
   ignoreGlobal?: boolean;
   /**
-   * if false then skip sourceMap generation for CommonJS modules
+   * If false, skips source map generation for CommonJS modules. This will improve performance.
    * @default true
    */
   sourceMap?: boolean;
   /**
-   * Instructs the plugin whether or not to enable mixed module transformations. This is useful in scenarios with mixed ES and CommonJS modules. Set to `true` if it's known that `require` calls should be transformed, or `false` if the code contains env detection and the `require` should survive a transformation.
+   * Instructs the plugin whether to enable mixed module transformations. This
+   * is useful in scenarios with modules that contain a mix of ES `import`
+   * statements and CommonJS `require` expressions. Set to `true` if `require`
+   * calls should be transformed to imports in mixed modules, or `false` if the
+   * `require` expressions should survive the transformation. The latter can be
+   * important if the code contains environment detection, or you are coding
+   * for an environment with special treatment for `require` calls such as
+   * ElectronJS. See also the `ignore` option.
    * @default false
    */
   transformMixedEsModules?: boolean;
   /**
-   * sometimes you have to leave require statements
-   * unconverted. Pass an array containing the IDs
-   * or a `id => boolean` function. Only use this
-   * option if you know what you're doing!
+   * Sometimes you have to leave require statements unconverted. Pass an array
+   * containing the IDs or a `id => boolean` function.
+   * @default []
+   */
+  ignore?: ReadonlyArray<string> | ((id: string) => boolean);
+  /**
+   * Controls how to render imports from external dependencies. By default,
+   * this plugin assumes that all external dependencies are CommonJS. This
+   * means they are rendered as default imports to be compatible with e.g.
+   * NodeJS where ES modules can only import a default export from a CommonJS
+   * dependency.
+   *
+   * If you set `esmExternals` to `true`, this plugins assumes that all
+   * external dependencies are ES modules and respect the
+   * `requireReturnsDefault` option. If that option is not set, they will be
+   * rendered as namespace imports.
+   *
+   * You can also supply an array of ids to be treated as ES modules, or a
+   * function that will be passed each external id to determine if it is an ES
+   * module.
+   * @default false
+   */
+  esmExternals?: boolean | ReadonlyArray<string> | ((id: string) => boolean);
+  /**
+   * Controls what is returned when requiring an ES module from a CommonJS file.
+   * When using the `esmExternals` option, this will also apply to external
+   * modules. By default, this plugin will render those imports as namespace
+   * imports. However there are some situations where this may not be desired.
+   * For these situations, you can change Rollup's behaviour either globally or
+   * per module. To change it globally, set the `requireReturnsDefault` option
+   * to one of the following values:
+   *
+   * - `false`: This is the default, requiring an ES module returns its
+   * namespace. For external dependencies when using `esmExternals: true`, no
+   * additional interop code is generated.
+   * - `"auto"`: This is complementary to how `output.exports: "auto"` works in
+   * Rollup: If a module has a default export and no named exports, requiring
+   * that module returns the default export. In all other cases, the namespace
+   * is returned. For external dependencies when using `esmExternals: true`, a
+   * corresponding interop helper is added.
+   * - `"preferred"`: If a module has a default export, requiring that module
+   * always returns the default export, no matter whether additional named
+   * exports exist. This is similar to how previous versions of this plugin
+   * worked. Again for external dependencies when using `esmExternals: true`, an
+   * interop helper is added.
+   * - `true`: This will always try to return the default export on require
+   * without checking if it actually exists. This can throw at build time if
+   * there is no default export. This is how external dependencies are handled
+   * when `esmExternals` is not used. The advantage over the other options is
+   * that, like `false`, this does not add an interop helper for external
+   * dependencies, keeping the code lean.
+   *
+   * To change this for individual modules, you can supply a function for
+   * `requireReturnsDefault` instead. This function will then be called once for
+   * each required ES module or external dependency with the corresponding id
+   * and allows you to return different values for different modules.
+   * @default false
    */
-  ignore?: ReadonlyArray<string | ((id: string) => boolean)>;
+  requireReturnsDefault?:
+    | RequireReturnsDefaultOption
+    | ((id: string) => RequireReturnsDefaultOption);
   /**
-   * Some modules contain dynamic `require` calls, or require modules that contain
-   *   circular dependencies, which are not handled well by static imports.
-   * Including those modules as `dynamicRequireTargets` will simulate a CommonJS (NodeJS-like)
-   *   environment for them with support for dynamic and circular dependencies.
+   * Some modules contain dynamic `require` calls, or require modules that
+   * contain circular dependencies, which are not handled well by static
+   * imports. Including those modules as `dynamicRequireTargets` will simulate a
+   * CommonJS (NodeJS-like)  environment for them with support for dynamic and
+   * circular dependencies.
    *
-   * Note: In extreme cases, this feature may result in some paths being rendered as
-   *   absolute in the final bundle. The plugin tries to avoid exposing paths from
-   *   the local machine, but if you are `dynamicRequirePaths` with paths that are
-   *   far away from your project's folder, that may require replacing strings
-   *   like `"/Users/John/Desktop/foo-project/"` -> `"/"`.
+   * Note: In extreme cases, this feature may result in some paths being
+   * rendered as absolute in the final bundle. The plugin tries to avoid
+   * exposing paths from the local machine, but if you are `dynamicRequirePaths`
+   * with paths that are far away from your project's folder, that may require
+   * replacing strings like `"/Users/John/Desktop/foo-project/"` -> `"/"`.
    */
   dynamicRequireTargets?: string | ReadonlyArray<string>;
 }