Added `Scope.getNames()` to avoid exposing internals.

src/Bundle.js

@@ -196,7 +196,7 @@ export default class Bundle {
 		});
 
 		if ( format !== 'es6' && exportMode === 'named' ) {
-			keys( this.exports.names )
+			this.exports.getNames()
 				.forEach( name => {
 					const canonicalName = this.exports.lookup( name ).name;
 
@@ -216,7 +216,7 @@ export default class Bundle {
 
 		// since we're rewriting variable exports, we want to
 		// ensure we don't try and export them again at the bottom
-		this.toExport = keys( this.exports.names )
+		this.toExport = this.exports.getNames()
 			.filter( key => !varExports[ key ] );
 
 		let magicString = new MagicString.Bundle({ separator: '\n\n' });
@@ -280,12 +280,17 @@ export default class Bundle {
 	}
 
 	sort () {
-		let seen = {};
+		// Set of visited module ids.
+		let seen = blank();
+
 		let ordered = [];
 		let hasCycles;
 
-		let strongDeps = {};
-		let stronglyDependsOn = {};
+		// Map from module id to list of modules.
+		let strongDeps = blank();
+
+		// Map from module id to boolean.
+		let stronglyDependsOn = blank();
 
 		function visit ( module ) {
 			seen[ module.id ] = true;

src/Scope.js

@@ -62,7 +62,7 @@ export default class Scope {
 
 		this.ids.filter( isntReference ).forEach( id => {
 			if ( typeof id === 'string' ) {
-				throw new Error( `Required name ${id} undefined!` );
+				throw new Error( `Required name "${id}" is undefined!` );
 			}
 
 			let name = id.name;
@@ -78,8 +78,8 @@ export default class Scope {
 
 	// Defines `name` in the scope to be `id`.
 	// If no `id` is supplied, a plain `Identifier` is created.
-	define ( name, id = new Identifier( name ) ) {
-		this.ids[ this.index( name ) ] = id;
+	define ( name, id ) {
+		this.ids[ this.index( name ) ] = id || new Identifier( name );
 	}
 
 	// TODO: rename! Too similar to `define`.
@@ -87,13 +87,18 @@ export default class Scope {
 		return name in this.names;
 	}
 
+	// Return the names referenced to in the scope.
+	getNames () {
+		return keys( this.names );
+	}
+
 	// *private, don't use*
 	//
 	// Return `name`'s index in the `ids` array if it exists,
 	// otherwise returns the index to a new placeholder slot.
 	index ( name ) {
 		if ( !( name in this.names ) ) {
-			return this.names[ name ] = this.ids.push( `"${name}"` ) - 1;
+			return this.names[ name ] = this.ids.push( name ) - 1;
 		}
 
 		return this.names[ name ];

src/finalisers/es6.js

@@ -1,7 +1,6 @@
-import { keys } from '../utils/object';
 
 function specifiersFor ( scope ) {
-	return keys( scope.names )
+	return scope.getNames()
 		.filter( notDefault )
 		.map( name => {
 			const id = scope.lookup( name );