diff --git a/package-lock.json b/package-lock.json
index 0944305e5..4df3da9a2 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4043,6 +4043,12 @@
         "is-symbol": "^1.0.2"
       }
     },
+    "esbuild": {
+      "version": "0.6.14",
+      "resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.6.14.tgz",
+      "integrity": "sha512-coT5T5flVNaleZQAciBJCpkJ0xB+7TShhinPLUK0Zbz/yy385DKY3nGTNmHy6+oFARI3qnNlBRAbMYgxLN9/mA==",
+      "dev": true
+    },
     "escape-goat": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/escape-goat/-/escape-goat-2.1.1.tgz",
diff --git a/package.json b/package.json
index 5c620f877..84a40d9af 100644
--- a/package.json
+++ b/package.json
@@ -101,6 +101,7 @@
 		"cssnano": "^4.1.10",
 		"devcert": "^1.1.2",
 		"es-module-lexer": "^0.3.24",
+		"esbuild": "^0.6.14",
 		"eslint": "^7.4.0",
 		"eslint-config-developit": "^1.2.0",
 		"eslint-config-prettier": "^6.11.0",
diff --git a/src/bundler.js b/src/bundler.js
index 083c5665f..6a8f0bd0a 100644
--- a/src/bundler.js
+++ b/src/bundler.js
@@ -18,6 +18,8 @@ import glob from 'tiny-glob';
 import aliasesPlugin from './plugins/aliases-plugin.js';
 import processGlobalPlugin from './plugins/process-global-plugin.js';
 import urlPlugin from './plugins/url-plugin.js';
+// import * as esbuild from 'esbuild';
+// import greenlet from './lib/greenlet.js';
 
 /** @param {string} p */
 const pathToPosix = p => p.split(sep).join(posix.sep);
@@ -213,11 +215,12 @@ export async function bundleProd({ cwd, publicDir, out, sourcemap, aliases, prof
 		preserveEntrySignatures: 'allow-extension',
 		manualChunks: npmChunks ? extractNpmChunks : undefined,
 		plugins: [
-			sucrasePlugin({
-				typescript: true,
-				sourcemap,
-				production: true
-			}),
+			// sucrasePlugin({
+			// 	typescript: true,
+			// 	sourcemap,
+			// 	production: true
+			// }),
+			terser({ compress: true, sourcemap }),
 			htmlEntriesPlugin({ cwd, publicDir, publicPath: '/' }),
 			publicPathPlugin({ publicPath: '/' }),
 			aliasesPlugin({ aliases }),
@@ -240,12 +243,9 @@ export async function bundleProd({ cwd, publicDir, out, sourcemap, aliases, prof
 		]
 	});
 
-	return await bundle.write({
-		entryFileNames: '[name].[hash].js',
-		chunkFileNames: 'chunks/[name].[hash].js',
-		assetFileNames: 'assets/[name].[hash][extname]',
+	const outputOptions = {
+		dir: out || 'dist',
 		compact: true,
-		plugins: [terser({ compress: true, sourcemap })],
 		sourcemap,
 		sourcemapPathTransform(p, mapPath) {
 			let url = pathToPosix(relative(cwd, resolve(dirname(mapPath), p)));
@@ -254,10 +254,69 @@ export async function bundleProd({ cwd, publicDir, out, sourcemap, aliases, prof
 			// replace internal npm prefix
 			url = url.replace(/^(\.?\.?\/)?[\b]npm\//, '@npm/');
 			return 'source:///' + url;
-		},
-		preferConst: true,
-		dir: out || 'dist'
+		}
+	};
+
+	const modern = bundle.write({
+		...outputOptions,
+		entryFileNames: '[name].[hash].js',
+		chunkFileNames: 'chunks/[name].[hash].js',
+		assetFileNames: 'assets/[name].[hash][extname]',
+		preferConst: true
+		// plugins: [terser({ compress: true, sourcemap })]
 	});
+
+	// const downlevel = greenlet(code => {
+	// 	const { transform } = require('sucrase');
+	// 	const out = transform(code, {
+	// 		transforms: ['typescript'],
+	// 		production: true
+	// 	});
+	// 	return out.code;
+	// });
+
+	// let esbuildService = ((esbuild && esbuild.default) || esbuild).startService();
+	// async function downlevel(code, fileName, sourcemap) {
+	// 	const start = Date.now();
+	// 	const { transform } = await esbuildService;
+	// 	const result = await transform(code, {
+	// 		define: {
+	// 			process: 'self',
+	// 			'process.env': 'self',
+	// 			'process.env.NODE_ENV': '"production"'
+	// 		},
+	// 		minify: true,
+	// 		sourcefile: fileName,
+	// 		sourcemap: sourcemap === true,
+	// 		strict: false,
+	// 		target: 'es2015' // es5 not supported (yet?)
+	// 	});
+	// 	console.log('esbuild(' + fileName + '): ', Date.now() - start);
+	// 	return { code: result.js, map: (sourcemap && result.jsSourceMap) || null };
+	// }
+
+	const legacy = bundle.write({
+		...outputOptions,
+		entryFileNames: '[name].[hash].legacy.js',
+		chunkFileNames: 'chunks/[name].[hash].legacy.js',
+		assetFileNames: 'assets/[name].[hash][extname]',
+		plugins: [
+			// {
+			// 	name: 'lazy-sucrase',
+			// 	async renderChunk(code, chunk) {
+			// 		return await downlevel(code, chunk.fileName);
+			// 	}
+			// }
+			// terser({ compress: true, sourcemap })
+		]
+	});
+
+	const results = await Promise.all([modern, legacy]);
+
+	// downlevel.terminate();
+	// (await esbuildService).stop();
+
+	return results[0];
 }
 
 /** @type {import('rollup').GetManualChunk} */
diff --git a/src/lib/esbuild-service.js b/src/lib/esbuild-service.js
new file mode 100644
index 000000000..31c4cff82
--- /dev/null
+++ b/src/lib/esbuild-service.js
@@ -0,0 +1,59 @@
+import * as esbuild from 'esbuild';
+
+/** @type {esbuild.Service} */
+let inst,
+	svc,
+	timer,
+	usage = 0;
+
+function free() {
+	if (--usage) return;
+	clearTimeout(timer);
+	timer = setTimeout(shutdown, 10);
+}
+
+function use() {
+	clearTimeout(timer);
+	usage++;
+}
+
+export function keepalive() {
+	use();
+	free();
+}
+
+export function shutdown() {
+	if (inst) inst.stop();
+	else if (svc) svc.then(inst => usage || inst.stop());
+	inst = svc = null;
+}
+process.on('beforeExit', shutdown);
+
+/**
+ * This function is the same shape as Terser.minify, except that it is async.
+ * @param {string} code
+ * @param {esbuild.TransformOptions} opts
+ */
+export async function transform(code, opts) {
+	if (!inst) {
+		if (!svc) {
+			svc = ((esbuild && esbuild.default) || esbuild).startService();
+		}
+		inst = await svc;
+	}
+	use();
+	try {
+		const result = await inst.transform(code, opts);
+		return {
+			code: result.js,
+			map: result.jsSourceMap || null,
+			warnings: result.warnings.map(warning => warning.text)
+		};
+	} catch (err) {
+		return {
+			error: err
+		};
+	} finally {
+		free();
+	}
+}
diff --git a/src/lib/greenlet.js b/src/lib/greenlet.js
new file mode 100644
index 000000000..b15d3a0c6
--- /dev/null
+++ b/src/lib/greenlet.js
@@ -0,0 +1,35 @@
+import { Worker } from 'worker_threads';
+
+/**
+ * @template {(...args: any) => any} T
+ * @param {T} fn
+ * @returns {(...args: Parameters<T>) => Promise<ReturnType<T> extends Promise<infer R> ? R : ReturnType<T>>}
+ */
+export default function greenlet(fn) {
+	let n = 0,
+		t = {};
+	function a(port, fn) {
+		port.on('message', ([id, params]) => {
+			try {
+				port.postMessage([id, 0, fn(...params)]);
+			} catch (e) {
+				port.postMessage([id, 1, (e && e.stack) || e + '']);
+			}
+		});
+	}
+	function g(...args) {
+		return new Promise((s, f) => ((t[++n] = [s, f]), w.postMessage([n, args])));
+	}
+	g.terminate = () => w.terminate();
+	let w = (g.worker = new Worker(`(${a})(require("worker_threads").parentPort,${fn})`, { eval: true }));
+	w.on('message', ([id, x, result]) => (t[id] = t[id][x](result)));
+	return g;
+}
+
+/** @param {string} a @param {number} b */
+function y(a, b) {
+	return 42;
+}
+const f = greenlet(y);
+
+f();
diff --git a/src/plugins/fast-minify.js b/src/plugins/fast-minify.js
index 8d2c96a9b..d470f92dd 100644
--- a/src/plugins/fast-minify.js
+++ b/src/plugins/fast-minify.js
@@ -1,30 +1,73 @@
-import terser from 'terser';
+// import terser from 'terser';
+import { transform, keepalive } from '../lib/esbuild-service.js';
+
+/**
+ * @param {import('rollup').PluginContext} rollupContext
+ * @param {{ code?: string, map?: any, warnings?: any[], error?: any }} result
+ */
+function normalizeResult(rollupContext, result) {
+	if (result.error) rollupContext.error(result.error);
+	if (result.warnings) for (const warn of result.warnings) rollupContext.warn(warn);
+	const map = result.map && typeof result.map === 'string' ? JSON.parse(result.map) : result.map || null;
+	return { code: result.code, map };
+}
 
 /** @returns {import('rollup').Plugin} */
 export default function fastMinifyPlugin({ sourcemap = false, warnThreshold = 50, compress = false } = {}) {
 	return {
 		name: 'fast-minify',
-		renderChunk(code, chunk) {
+		buildStart() {
+			keepalive();
+		},
+		async transform(code, id) {
+			if (!/\.tsx?$/.test(id)) return null;
+			const out = await transform(code, {
+				loader: 'tsx',
+				minify: false,
+				sourcefile: id,
+				sourcemap: false,
+				strict: false
+			});
+			return normalizeResult(this, out);
+		},
+		async renderChunk(code, chunk) {
 			const start = Date.now();
-			const out = terser.minify(code, {
-				sourceMap: sourcemap,
-				mangle: true,
-				compress,
-				module: true,
-				ecma: 9,
-				safari10: true,
-				output: {
-					comments: false
-				}
+
+			const out = await transform(code, {
+				define: {
+					process: 'self',
+					'process.env': 'self',
+					'process.env.NODE_ENV': '"production"'
+				},
+				minify: !!compress,
+				sourcefile: chunk.fileName,
+				sourcemap: sourcemap === true,
+				strict: false,
+				target: 'es6'
+				// target: 'es2015' // es5 not supported (yet?)
 			});
+
+			// const out = terser.minify(code, {
+			// 	sourceMap: sourcemap,
+			// 	mangle: true,
+			// 	compress: compress && {
+			// 		// passes: 2,
+			// 		...(compress === true ? {} : compress)
+			// 	},
+			// 	module: true,
+			// 	ecma: 9,
+			// 	safari10: true,
+			// 	output: {
+			// 		comments: false
+			// 	}
+			// });
+
 			const duration = Date.now() - start;
-			if (out.error) this.error(out.error);
-			if (out.warnings) for (const warn of out.warnings) this.warn(warn);
 			if (duration > warnThreshold) {
 				this.warn(`minify(${chunk.fileName}) took ${duration}ms`);
 			}
-			const map = typeof out.map === 'string' ? JSON.parse(out.map) : out.map || null;
-			return { code: out.code, map };
+
+			return normalizeResult(this, out);
 		}
 	};
 }