wrap ES modules in an IIFE

src/generators/Generator.ts

@@ -302,7 +302,7 @@ export default class Generator {
 		return (expression._dependencies = dependencies);
 	}
 
-	generate(result: string, options: CompileOptions, { name, format }: GenerateOptions ) {
+	generate(result: string, options: CompileOptions, { banner = '', name, format }: GenerateOptions ) {
 		const pattern = /\[✂(\d+)-(\d+)$/;
 
 		const parts = result.split('✂]');
@@ -318,7 +318,7 @@ export default class Generator {
 
 		const { intro, outro } = getModuleWrapper(format, name, options, this.imports, this.source);
 
-		addString(intro + '\n\n');
+		addString(banner + intro + '\n\n');
 
 		const { filename } = options;
 

src/generators/dom/index.ts

@@ -326,6 +326,8 @@ export default function dom(
 			return generator.alias(name);
 		});
 
+	let banner = `/* ${options.filename ? `${options.filename} ` : ``}generated by Svelte v${version} */\n`;
+
 	if (sharedPath) {
 		const used = Array.from(usedHelpers).sort();
 		if (format === 'es') {
@@ -334,9 +336,7 @@ export default function dom(
 				return name !== alias ? `${name} as ${alias}` : name;
 			});
 
-			result =
-				`import { ${names.join(', ')} } from ${JSON.stringify(sharedPath)};\n\n` +
-				result;
+			banner += `import { ${names.join(', ')} } from ${JSON.stringify(sharedPath)};\n\n`;
 		}
 
 		else if (format === 'cjs') {
@@ -347,7 +347,7 @@ export default function dom(
 				requires += `\nvar ${alias} = ${SHARED}.${name};`;
 			});
 
-			result = `${requires}\n\n${result}`;
+			banner += requires + '\n\n';
 		}
 
 		else {
@@ -391,20 +391,19 @@ export default function dom(
 				// special case
 				const global = `_svelteTransitionManager`;
 
-				result += `\n\nvar ${generator.alias('transitionManager')} = window.${global} || (window.${global} = ${code});`;
+				banner += `\n\nvar ${generator.alias('transitionManager')} = window.${global} || (window.${global} = ${code});`;
 			} else {
 				const alias = generator.alias(expression.id.name);
 				if (alias !== expression.id.name)
 					code.overwrite(expression.id.start, expression.id.end, alias);
 
-				result += `\n\n${code}`;
+				banner += `\n\n${code}`;
 			}
 		});
 	}
 
-	result = `/* ${options.filename ? `${options.filename} ` : ``}generated by Svelte v${version} */\n\n${result}`;
-
 	return generator.generate(result, options, {
+		banner,
 		name,
 		format,
 	});

src/generators/shared/utils/getModuleWrapper.ts

@@ -68,8 +68,14 @@ function getEsWrapper(name: string, options: CompileOptions, imports: Node[], so
 		.join('\n');
 
 	return {
-		intro: importBlock ? importBlock + '\n\n' : '',
-		outro: `export default ${name};`
+		intro: deindent`
+			${importBlock}
+
+			export default (function() {
+		`,
+		outro: deindent`
+			return ${name};
+			}());`
 	};
 }
 

src/interfaces.ts

@@ -64,6 +64,7 @@ export interface CompileOptions {
 export interface GenerateOptions {
 	name: string;
 	format: ModuleFormat;
+	banner?: string;
 }
 
 export interface Visitor {

test/runtime/index.js

@@ -73,11 +73,12 @@ describe("runtime", () => {
 					);
 					const { code } = svelte.compile(source, compileOptions);
 					const startIndex = code.indexOf("function create_main_fragment"); // may change!
-					if (startIndex === -1)
-						throw new Error("missing create_main_fragment");
+					if (startIndex === -1) throw new Error("missing create_main_fragment");
+					const endIndex = code.lastIndexOf("return");
 					const es5 =
 						code.slice(0, startIndex).split('\n').map(x => spaces(x.length)).join('\n') +
-						code.slice(startIndex).replace(/export default .+/, "");
+						code.slice(startIndex, endIndex);
+
 					acorn.parse(es5, { ecmaVersion: 5 });
 
 					if (/Object\.assign/.test(es5)) {