don't overwrite globals

src/transform.js

@@ -230,14 +230,11 @@ export default function transformCommonjs ( code, id, isEntry, ignoreGlobal, cus
 	const name = getName( id );
 
 	function addExport ( x ) {
-		let declaration;
+		const deconflicted = deconflict( scope, globals, name );
 
-		if ( x === name ) {
-			const deconflicted = deconflict( scope, globals, name );
-			declaration = `var ${deconflicted} = ${moduleName}.${x};\nexport { ${deconflicted} as ${x} };`;
-		} else {
-			declaration = `export var ${x} = ${moduleName}.${x};`;
-		}
+		const declaration = deconflicted === name ?
+			`export var ${x} = ${moduleName}.${x};` :
+			`var ${deconflicted} = ${moduleName}.${x};\nexport { ${deconflicted} as ${x} };`;
 
 		namedExportDeclarations.push( declaration );
 	}

test/function/global-not-overwritten/_config.js

@@ -0,0 +1,7 @@
+const assert = require( 'assert' );
+
+module.exports = {
+	exports: function ( exports ) {
+		assert.equal( exports.encoded, encodeURIComponent( 'test string' ) );
+	}
+};

test/function/global-not-overwritten/encode.js

@@ -0,0 +1,5 @@
+exports.encodeURIComponent = function () {
+	return encodeURIComponent( this.str );
+};
+
+console.log( exports ); // to ensure module is wrapped

test/function/global-not-overwritten/main.js

@@ -0,0 +1,8 @@
+import { encodeURIComponent } from './encode.js';
+
+var foo = {
+	str: 'test string',
+	encodeURIComponent
+};
+
+export var encoded = foo.encodeURIComponent();