Switch to ES2015 output

rollup.config.js

@@ -84,8 +84,8 @@ export default command => {
 				alias(moduleAliases),
 				resolve(),
 				json(),
-				typescript(),
 				commonjs({ include: 'node_modules/**', namedExports: { micromatch: ['matcher'] } }),
+				typescript({include: '**/*.{ts,js}'}),
 				fixAcornEsmImport()
 			],
 			// acorn needs to be external as some plugins rely on a shared acorn instance
@@ -108,8 +108,8 @@ export default command => {
 				resolve(),
 				json(),
 				string({ include: '**/*.md' }),
-				typescript(),
-				commonjs({ include: 'node_modules/**' })
+				commonjs({ include: 'node_modules/**' }),
+				typescript({include: '**/*.{ts,js}'}),
 			],
 			external: ['fs', 'path', 'module', 'events', 'rollup', 'assert', 'os', 'util'],
 			treeshake: {
@@ -145,8 +145,8 @@ export default command => {
 						if (~id.indexOf('path.ts')) return fs.readFileSync('browser/path.ts', 'utf-8');
 					}
 				},
-				typescript(),
 				commonjs(),
+				typescript({include: '**/*.{ts,js}'}),
 				terser({ module: true, output: { comments: 'some' } })
 			],
 			treeshake: {

src/Chunk.ts

@@ -186,11 +186,10 @@ export default class Chunk {
 			module
 		}));
 		for (const { map } of exportVariableMaps) {
-			for (const exposedVariable of Array.from(map.keys())) {
+			for (const exposedVariable of map.keys()) {
 				this.exports.add(exposedVariable);
 			}
 		}
-		const exposedVariables = Array.from(this.exports);
 		checkNextEntryModule: for (const { map, module } of exportVariableMaps) {
 			if (!this.graph.preserveModules) {
 				if (
@@ -200,14 +199,14 @@ export default class Chunk {
 				) {
 					continue checkNextEntryModule;
 				}
-				for (const exposedVariable of exposedVariables) {
+				for (const exposedVariable of this.exports) {
 					if (!map.has(exposedVariable)) {
 						continue checkNextEntryModule;
 					}
 				}
 			}
 			this.facadeModule = module;
-			for (const [variable, exportNames] of Array.from(map)) {
+			for (const [variable, exportNames] of map) {
 				for (const exportName of exportNames) {
 					this.exportNames[exportName] = variable;
 				}
@@ -260,9 +259,8 @@ export default class Chunk {
 			safeExportName: string;
 		this.exportNames = Object.create(null);
 		this.sortedExportNames = null;
-		const exportedVariables = Array.from(this.exports);
 		if (mangle) {
-			for (const variable of exportedVariables) {
+			for (const variable of this.exports) {
 				do {
 					safeExportName = toBase64(++i);
 					// skip past leading number identifiers
@@ -274,7 +272,7 @@ export default class Chunk {
 				this.exportNames[safeExportName] = variable;
 			}
 		} else {
-			for (const variable of exportedVariables) {
+			for (const variable of this.exports) {
 				i = 0;
 				safeExportName = variable.name;
 				while (this.exportNames[safeExportName]) {
@@ -361,15 +359,15 @@ export default class Chunk {
 			this.orderedModules.push(module);
 		}
 
-		for (const variable of Array.from(chunk.imports)) {
+		for (const variable of chunk.imports) {
 			if (!this.imports.has(variable) && variable.module.chunk !== this) {
 				this.imports.add(variable);
 			}
 		}
 
 		// NB detect when exported variables are orphaned by the merge itself
 		// (involves reverse tracing dependents)
-		for (const variable of Array.from(chunk.exports)) {
+		for (const variable of chunk.exports) {
 			if (!this.exports.has(variable)) {
 				this.exports.add(variable);
 			}
@@ -475,7 +473,7 @@ export default class Chunk {
 		};
 
 		// Make sure the direct dependencies of a chunk are present to maintain execution order
-		for (const { module } of Array.from(this.imports)) {
+		for (const { module } of this.imports) {
 			const chunkOrExternal = module instanceof Module ? module.chunk : module;
 			if (this.dependencies.indexOf(chunkOrExternal) === -1) {
 				this.dependencies.push(chunkOrExternal);
@@ -863,13 +861,12 @@ export default class Chunk {
 			exportDeclaration.push({ imported: importName, reexported: exportName, needsLiveBinding });
 		}
 
-		const importsAsArray = Array.from(this.imports);
 		const renderedImports = new Set<Variable>();
 		const dependencies: ChunkDependencies = [];
 
 		for (const dep of this.dependencies) {
 			const imports: ImportSpecifier[] = [];
-			for (const variable of importsAsArray) {
+			for (const variable of this.imports) {
 				const renderedVariable =
 					variable instanceof ExportDefaultVariable && variable.referencesOriginal()
 						? variable.getOriginalVariable()
@@ -1071,7 +1068,7 @@ export default class Chunk {
 	}
 
 	private setUpModuleImports(module: Module) {
-		for (const variable of Array.from(module.imports)) {
+		for (const variable of module.imports) {
 			if (variable.module.chunk !== this) {
 				this.imports.add(variable);
 				if (variable.module instanceof Module) {

src/Graph.ts

@@ -217,7 +217,7 @@ export default class Graph {
 			if (entryModules.length === 0) {
 				throw new Error('You must supply options.input to rollup');
 			}
-			for (const module of Array.from(this.moduleById.values())) {
+			for (const module of this.moduleById.values()) {
 				if (module instanceof Module) {
 					this.modules.push(module);
 					this.watchFiles[module.id] = true;

src/utils/deconflictChunk.ts

@@ -70,7 +70,7 @@ function deconflictImportsEsm(
 	_dependencies: (ExternalModule | Chunk)[],
 	interop: boolean
 ) {
-	for (const variable of Array.from(imports)) {
+	for (const variable of imports) {
 		const module = variable.module;
 		const name = variable.name;
 		let proposedName: string;
@@ -97,7 +97,7 @@ function deconflictImportsOther(
 	for (const chunkOrExternalModule of dependencies) {
 		chunkOrExternalModule.variableName = getSafeName(chunkOrExternalModule.variableName, usedNames);
 	}
-	for (const variable of Array.from(imports)) {
+	for (const variable of imports) {
 		const module = variable.module;
 		if (module instanceof ExternalModule) {
 			const name = variable.name;

tsconfig.json

@@ -2,8 +2,7 @@
     "compilerOptions": {
         "allowSyntheticDefaultImports": true,
         "diagnostics": true,
-        "downlevelIteration": false,
-        "lib": ["es5", "es6", "dom"],
+        "lib": ["es6", "dom"],
         "module": "commonjs",
         "noEmitOnError": true,
         "noImplicitAny": true,
@@ -12,7 +11,7 @@
         "noUnusedParameters": true,
         "pretty": true,
         "skipLibCheck": true,
-        "target": "es5"
+        "target": "es2015"
     },
     "include": [
         "typings/**/*.d.ts",