@typhonjs-build-test/rollup-plugin-pkg-imports

Provides two Rollup plugins that resolve import specifiers defined in package.json imports that link other NPM packages.

• importsExternal - Resolves NPM packages from import specifiers substituting the fully qualified name in addition to adding a regular expression to the Rollup external configuration.

• importsResolve - Resolves NPM package paths to the associated import specifier.

API documentation

Overview

These plugins are useful for library authors and general developers for a variety of use cases. importsExternal in particular is helpful when developing packages that have peer dependencies that are not directly bundled into the library package or dependencies between sub-path exports. Both plugins are similar to @rollup/plugin-node-resolve and function as a resolution source to resolve internal imports from package.json.

importsExternal in particular automatically constructs regular expressions added to the Rollup external configuration array in addition to resolving against the value provided for each activated imports entry. You may use globs in defining the imports entries allowing targeting of external peer dependency packages that have sub-path exports.

By default, all imports entries that refer to a local path starting with . are ignored.

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Examples importsExternal:

Example #1 package.json imports entry:

{
  "imports": {
    "#shortname/*": "@my-org-name/a-long-package-name/*"
  },
  "peerDependencies": {
    "@my-org-name/a-long-package-name": ">=1.0.0"
  }
}

Above the #shortname/* is a shortened import key for @my-org-name/a-long-package-name. You can abbreviate the keys however you like. This allows the use of import { thing } from '#shortname/thing'; rather than the fully qualified name: import { thing } from '@my-org-name/a-long-package-name/thing';.

Variation on Example #1:

When developing a package with sub-path exports where there are cross-linked dependencies between various sub-path exports you can map an import specifier to the local package. When independently bundling each sub-path export importsExternal will automatically handle creating the appropriate Rollup external configuration to exclude bundling cross-linked sub-path exports together.

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Example Rollup configuration object

// Both of the following packages are optional.
import resolve             from '@rollup/plugin-node-resolve';
import { generateDTS }     from '@typhonjs-build-test/esm-d-ts';

import { importsExternal } from '@typhonjs-build-test/rollup-plugin-pkg-imports';

const rollupConfig = {
   input: 'src/index.js',
   output: {
      file: 'dist/index.js',
      format: 'esm'
   },
   plugins: [
      importsExternal(),
      resolve(),  // Use `importsExternal` before `@rollup/plugin-node-resolve`.
      generateDTS.plugin() // Optional use of `@typhonjs-build-test/esm-d-ts`.
   ]
}

By default the closest package.json from the Rollup configuration input source is automatically loaded and all imports are processed as external.

You may provide a configuration object to importsExternal with the following entries:

Attribute	Type	Description
importsKeys	string[]	Only target the provided imports keys.
packageObj	object	A specific package.json object to use.

---

Usage inside a ESM JS source file (./src/index.js):

import { something } from '#shortname/sub-path';

#shortname/sub-path is connected to @my-external-package/a-long-package-name/sub-path and is not included in the bundled output.

---

Example importsResolve:

Example #2 package.json imports entry:

{
  "imports": {
    "#shortname/*": "@my-org-name/a-long-package-name/*"
  }
}

Above the #shortname/* is a shortened import key for @my-org-name/a-long-package-name. You can abbreviate the keys however you like. This allows the use of import { thing } from '#shortname/thing'; rather than the fully qualified name: import { thing } from '@my-org-name/a-long-package-name/thing';.

Essentially, importsResolve is a convenience mechanism when using Rollup to automatically resolve import specifiers. The referenced packages are included in the bundle generated without having to manually configure @rollup/plugin-replace or @rollup/plugin-alias.

Additionally, you may provide a string array exportConditions in the plugin options to resolve specific export conditions. The default is ['node', 'import', 'default'].

For instance if you are using Vite 4.2+ import specifiers are automatically resolved in production / Rollup builds. This plugin functions in a similar manner, but handy for direct Rollup builds.

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Synergies

If you are working on ES Modules / modern Javascript and document your code with JSDoc a great optional Rollup plugin and tool to use is @typhonjs-build-test/esm-d-ts. The Rollup plugin for esm-d-ts automatically creates bundled TS declarations from ESM source and is aware of rollup-plugin-pkg-imports allowing the generated TS declarations to include the correct mapped packages.

Roadmap / TODO

• Evaluate any concerns for mono-repo use cases.
• Create a comprehensive testsuite; rest assured though as these plugins are used in production environments.