add interop blocks for default imports from external modules

src/finalisers/amd.js

@@ -1,4 +1,5 @@
 import { getName, quoteId } from '../utils/map-helpers';
+import getInteropBlock from './shared/getInteropBlock';
 
 export default function amd ( bundle, magicString, { exportMode, indentString }, options ) {
 	let deps = bundle.externalModules.map( quoteId );
@@ -15,6 +16,10 @@ export default function amd ( bundle, magicString, { exportMode, indentString },
 
 	const intro = `define(${params}function (${args.join( ', ' )}) { 'use strict';\n\n`;
 
+	// var foo__default = 'default' in foo ? foo['default'] : foo;
+	const interopBlock = getInteropBlock( bundle );
+	if ( interopBlock ) magicString.prepend( interopBlock + '\n\n' );
+
 	const exports = bundle.entryModule.exports;
 
 	let exportBlock;
@@ -27,9 +32,7 @@ export default function amd ( bundle, magicString, { exportMode, indentString },
 		}).join( '\n' );
 	}
 
-	if ( exportBlock ) {
+	if ( exportBlock ) magicString.append( '\n\n' + exportBlock );
-		magicString.append( '\n\n' + exportBlock );
-	}
 
 	return magicString
 		.indent( indentString )

src/finalisers/es6.js

@@ -1,7 +1,42 @@
 import { keys } from '../utils/object';
 
 export default function es6 ( bundle, magicString, { exportMode }, options ) {
-	const introBlock = ''; // TODO...
+	const importBlock = bundle.externalModules
+		.map( module => {
+			let defaultSpecifier = null;
+			let namedSpecifiers = null;
+
+			if ( module.needsDefault ) {
+				const defaultImportDeclaration = module.importedByBundle.filter( declaration => declaration.name === 'default' )[0];
+				defaultSpecifier = defaultImportDeclaration.localName;
+			}
+
+			if ( module.needsNamed ) {
+				namedSpecifiers = '{ ' + module.importedByBundle
+					.filter( declaration => declaration.name !== 'default' )
+					.map( declaration => {
+						const { name, localName } = declaration;
+
+						return name === localName ?
+							name :
+							`${name} as ${localName}`;
+					})
+					.join( ', ' ) + ' }';
+			}
+
+			const specifiers = module.needsDefault && module.needsNamed ?
+				`${defaultSpecifier}, ${namedSpecifiers}` :
+				( defaultSpecifier || namedSpecifiers );
+
+			return specifiers ?
+				`import ${specifiers} from '${module.id}';` :
+				`import '${module.id}';`;
+		})
+		.join( '\n' );
+
+	if ( importBlock ) {
+		magicString.prepend( importBlock + '\n\n' );
+	}
 
 	const exports = bundle.entryModule.exports;
 	const exportBlock = keys( exports ).map( exportedName => {

src/finalisers/iife.js

@@ -1,5 +1,6 @@
 import { blank } from '../utils/object';
 import { getName } from '../utils/map-helpers';
+import getInteropBlock from './shared/getInteropBlock';
 
 export default function iife ( bundle, magicString, { exportMode, indentString }, options ) {
 	const globalNames = options.globals || blank();
@@ -22,6 +23,10 @@ export default function iife ( bundle, magicString, { exportMode, indentString }
 	let intro = `(function (${args}) { 'use strict';\n\n`;
 	let outro = `\n\n})(${dependencies});`;
 
+	// var foo__default = 'default' in foo ? foo['default'] : foo;
+	const interopBlock = getInteropBlock( bundle );
+	if ( interopBlock ) magicString.prepend( interopBlock + '\n\n' );
+
 	if ( exportMode === 'default' ) {
 		intro = `var ${options.moduleName} = ${intro}`;
 		magicString.append( `\n\nreturn ${bundle.entryModule.getCanonicalName('default')};` );

src/finalisers/shared/getInteropBlock.js

@@ -0,0 +1,6 @@
+export default function getInteropBlock ( bundle ) {
+	return bundle.externalModules
+		.filter( module => module.needsDefault && module.needsNamed )
+		.map( module => `var ${module.name}__default = 'default' in ${module.name} ? ${module.name}['default'] : ${module.name};` )
+		.join( '\n' );
+}

src/finalisers/umd.js

@@ -1,5 +1,6 @@
 import { blank } from '../utils/object';
 import { getName, quoteId, req } from '../utils/map-helpers';
+import getInteropBlock from './shared/getInteropBlock';
 
 export default function umd ( bundle, magicString, { exportMode, indentString }, options ) {
 	if ( exportMode !== 'none' && !options.moduleName ) {
@@ -40,6 +41,10 @@ export default function umd ( bundle, magicString, { exportMode, indentString },
 
 		`.replace( /^\t\t/gm, '' ).replace( /^\t/gm, magicString.getIndentString() );
 
+	// var foo__default = 'default' in foo ? foo['default'] : foo;
+	const interopBlock = getInteropBlock( bundle );
+	if ( interopBlock ) magicString.prepend( interopBlock + '\n\n' );
+
 	const exports = bundle.entryModule.exports;
 
 	let exportBlock;