feat(): dedupe accepts a function (#225)

* feat(): dedupe accepts a function

* Add test and shouldDedupe

index.d.ts

@@ -85,7 +85,7 @@ export interface Options {
 	 * to prevent bundling the same package multiple times if package is
 	 * imported from dependencies.
 	 */
-	dedupe?: string[];
+	dedupe?: string[] | ((importee: string) => boolean);
 
 	/**
 	 * Any additional options that should be passed through

src/index.js

@@ -130,6 +130,10 @@ export default function nodeResolve ( options = {} ) {
 	const extensions = options.extensions || DEFAULT_EXTS;
 	const packageInfoCache = new Map();
 
+	const shouldDedupe = typeof dedupe === 'function'
+		? dedupe
+		: importee => dedupe.includes(importee);
+
 	function getCachedPackageInfo (pkg, pkgPath) {
 		if (packageInfoCache.has(pkgPath)) {
 			return packageInfoCache.get(pkgPath);
@@ -216,7 +220,7 @@ export default function nodeResolve ( options = {} ) {
 
 			const basedir = importer ? dirname( importer ) : process.cwd();
 
-			if (dedupe.indexOf(importee) !== -1) {
+			if (shouldDedupe(importee)) {
 				importee = join(process.cwd(), 'node_modules', importee);
 			}
 

test/test.js

@@ -880,6 +880,22 @@ describe( 'rollup-plugin-node-resolve', function () {
 		});
 	});
 
+	it( 'single module version is bundle if dedupe is set as a function', () => {
+		return rollup.rollup({
+			input: 'samples/react-app/main.js',
+			plugins: [
+				nodeResolve({
+					dedupe: (dep) => dep === 'react'
+				})
+			]
+		}).then( executeBundle ).then( module => {
+			assert.deepEqual(module.exports, {
+				React: 'react:root',
+				ReactConsumer: 'react-consumer:react:root'
+			});
+		});
+	});
+
 	it( 'multiple module versions are bundled if dedupe is not set', () => {
 		return rollup.rollup({
 			input: 'samples/react-app/main.js',