diff --git a/events.mjs b/events.mjs
new file mode 100644
index 0000000..556a29a
--- /dev/null
+++ b/events.mjs
@@ -0,0 +1,496 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+'use strict';
+
+var R = typeof Reflect === 'object' ? Reflect : null
+var ReflectApply = R && typeof R.apply === 'function'
+  ? R.apply
+  : function ReflectApply(target, receiver, args) {
+    return Function.prototype.apply.call(target, receiver, args);
+  }
+
+var ReflectOwnKeys
+if (R && typeof R.ownKeys === 'function') {
+  ReflectOwnKeys = R.ownKeys
+} else if (Object.getOwnPropertySymbols) {
+  ReflectOwnKeys = function ReflectOwnKeys(target) {
+    return Object.getOwnPropertyNames(target)
+      .concat(Object.getOwnPropertySymbols(target));
+  };
+} else {
+  ReflectOwnKeys = function ReflectOwnKeys(target) {
+    return Object.getOwnPropertyNames(target);
+  };
+}
+
+function ProcessEmitWarning(warning) {
+  if (console && console.warn) console.warn(warning);
+}
+
+var NumberIsNaN = Number.isNaN || function NumberIsNaN(value) {
+  return value !== value;
+}
+
+function EventEmitter() {
+  EventEmitter.init.call(this);
+}
+export default EventEmitter;
+
+// Backwards-compat with node 0.10.x
+EventEmitter.EventEmitter = EventEmitter;
+
+EventEmitter.prototype._events = undefined;
+EventEmitter.prototype._eventsCount = 0;
+EventEmitter.prototype._maxListeners = undefined;
+
+// By default EventEmitters will print a warning if more than 10 listeners are
+// added to it. This is a useful default which helps finding memory leaks.
+var defaultMaxListeners = 10;
+
+function checkListener(listener) {
+  if (typeof listener !== 'function') {
+    throw new TypeError('The "listener" argument must be of type Function. Received type ' + typeof listener);
+  }
+}
+
+Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
+  enumerable: true,
+  get: function() {
+    return defaultMaxListeners;
+  },
+  set: function(arg) {
+    if (typeof arg !== 'number' || arg < 0 || NumberIsNaN(arg)) {
+      throw new RangeError('The value of "defaultMaxListeners" is out of range. It must be a non-negative number. Received ' + arg + '.');
+    }
+    defaultMaxListeners = arg;
+  }
+});
+
+EventEmitter.init = function() {
+
+  if (this._events === undefined ||
+      this._events === Object.getPrototypeOf(this)._events) {
+    this._events = Object.create(null);
+    this._eventsCount = 0;
+  }
+
+  this._maxListeners = this._maxListeners || undefined;
+};
+
+// Obviously not all Emitters should be limited to 10. This function allows
+// that to be increased. Set to zero for unlimited.
+EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
+  if (typeof n !== 'number' || n < 0 || NumberIsNaN(n)) {
+    throw new RangeError('The value of "n" is out of range. It must be a non-negative number. Received ' + n + '.');
+  }
+  this._maxListeners = n;
+  return this;
+};
+
+function _getMaxListeners(that) {
+  if (that._maxListeners === undefined)
+    return EventEmitter.defaultMaxListeners;
+  return that._maxListeners;
+}
+
+EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
+  return _getMaxListeners(this);
+};
+
+EventEmitter.prototype.emit = function emit(type) {
+  var args = [];
+  for (var i = 1; i < arguments.length; i++) args.push(arguments[i]);
+  var doError = (type === 'error');
+
+  var events = this._events;
+  if (events !== undefined)
+    doError = (doError && events.error === undefined);
+  else if (!doError)
+    return false;
+
+  // If there is no 'error' event listener then throw.
+  if (doError) {
+    var er;
+    if (args.length > 0)
+      er = args[0];
+    if (er instanceof Error) {
+      // Note: The comments on the `throw` lines are intentional, they show
+      // up in Node's output if this results in an unhandled exception.
+      throw er; // Unhandled 'error' event
+    }
+    // At least give some kind of context to the user
+    var err = new Error('Unhandled error.' + (er ? ' (' + er.message + ')' : ''));
+    err.context = er;
+    throw err; // Unhandled 'error' event
+  }
+
+  var handler = events[type];
+
+  if (handler === undefined)
+    return false;
+
+  if (typeof handler === 'function') {
+    ReflectApply(handler, this, args);
+  } else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      ReflectApply(listeners[i], this, args);
+  }
+
+  return true;
+};
+
+function _addListener(target, type, listener, prepend) {
+  var m;
+  var events;
+  var existing;
+
+  checkListener(listener);
+
+  events = target._events;
+  if (events === undefined) {
+    events = target._events = Object.create(null);
+    target._eventsCount = 0;
+  } else {
+    // To avoid recursion in the case that type === "newListener"! Before
+    // adding it to the listeners, first emit "newListener".
+    if (events.newListener !== undefined) {
+      target.emit('newListener', type,
+                  listener.listener ? listener.listener : listener);
+
+      // Re-assign `events` because a newListener handler could have caused the
+      // this._events to be assigned to a new object
+      events = target._events;
+    }
+    existing = events[type];
+  }
+
+  if (existing === undefined) {
+    // Optimize the case of one listener. Don't need the extra array object.
+    existing = events[type] = listener;
+    ++target._eventsCount;
+  } else {
+    if (typeof existing === 'function') {
+      // Adding the second element, need to change to array.
+      existing = events[type] =
+        prepend ? [listener, existing] : [existing, listener];
+      // If we've already got an array, just append.
+    } else if (prepend) {
+      existing.unshift(listener);
+    } else {
+      existing.push(listener);
+    }
+
+    // Check for listener leak
+    m = _getMaxListeners(target);
+    if (m > 0 && existing.length > m && !existing.warned) {
+      existing.warned = true;
+      // No error code for this since it is a Warning
+      // eslint-disable-next-line no-restricted-syntax
+      var w = new Error('Possible EventEmitter memory leak detected. ' +
+                          existing.length + ' ' + String(type) + ' listeners ' +
+                          'added. Use emitter.setMaxListeners() to ' +
+                          'increase limit');
+      w.name = 'MaxListenersExceededWarning';
+      w.emitter = target;
+      w.type = type;
+      w.count = existing.length;
+      ProcessEmitWarning(w);
+    }
+  }
+
+  return target;
+}
+
+EventEmitter.prototype.addListener = function addListener(type, listener) {
+  return _addListener(this, type, listener, false);
+};
+
+EventEmitter.prototype.on = EventEmitter.prototype.addListener;
+
+EventEmitter.prototype.prependListener =
+    function prependListener(type, listener) {
+      return _addListener(this, type, listener, true);
+    };
+
+function onceWrapper() {
+  if (!this.fired) {
+    this.target.removeListener(this.type, this.wrapFn);
+    this.fired = true;
+    if (arguments.length === 0)
+      return this.listener.call(this.target);
+    return this.listener.apply(this.target, arguments);
+  }
+}
+
+function _onceWrap(target, type, listener) {
+  var state = { fired: false, wrapFn: undefined, target: target, type: type, listener: listener };
+  var wrapped = onceWrapper.bind(state);
+  wrapped.listener = listener;
+  state.wrapFn = wrapped;
+  return wrapped;
+}
+
+EventEmitter.prototype.once = function once(type, listener) {
+  checkListener(listener);
+  this.on(type, _onceWrap(this, type, listener));
+  return this;
+};
+
+EventEmitter.prototype.prependOnceListener =
+    function prependOnceListener(type, listener) {
+      checkListener(listener);
+      this.prependListener(type, _onceWrap(this, type, listener));
+      return this;
+    };
+
+// Emits a 'removeListener' event if and only if the listener was removed.
+EventEmitter.prototype.removeListener =
+    function removeListener(type, listener) {
+      var list, events, position, i, originalListener;
+
+      checkListener(listener);
+
+      events = this._events;
+      if (events === undefined)
+        return this;
+
+      list = events[type];
+      if (list === undefined)
+        return this;
+
+      if (list === listener || list.listener === listener) {
+        if (--this._eventsCount === 0)
+          this._events = Object.create(null);
+        else {
+          delete events[type];
+          if (events.removeListener)
+            this.emit('removeListener', type, list.listener || listener);
+        }
+      } else if (typeof list !== 'function') {
+        position = -1;
+
+        for (i = list.length - 1; i >= 0; i--) {
+          if (list[i] === listener || list[i].listener === listener) {
+            originalListener = list[i].listener;
+            position = i;
+            break;
+          }
+        }
+
+        if (position < 0)
+          return this;
+
+        if (position === 0)
+          list.shift();
+        else {
+          spliceOne(list, position);
+        }
+
+        if (list.length === 1)
+          events[type] = list[0];
+
+        if (events.removeListener !== undefined)
+          this.emit('removeListener', type, originalListener || listener);
+      }
+
+      return this;
+    };
+
+EventEmitter.prototype.off = EventEmitter.prototype.removeListener;
+
+EventEmitter.prototype.removeAllListeners =
+    function removeAllListeners(type) {
+      var listeners, events, i;
+
+      events = this._events;
+      if (events === undefined)
+        return this;
+
+      // not listening for removeListener, no need to emit
+      if (events.removeListener === undefined) {
+        if (arguments.length === 0) {
+          this._events = Object.create(null);
+          this._eventsCount = 0;
+        } else if (events[type] !== undefined) {
+          if (--this._eventsCount === 0)
+            this._events = Object.create(null);
+          else
+            delete events[type];
+        }
+        return this;
+      }
+
+      // emit removeListener for all listeners on all events
+      if (arguments.length === 0) {
+        var keys = Object.keys(events);
+        var key;
+        for (i = 0; i < keys.length; ++i) {
+          key = keys[i];
+          if (key === 'removeListener') continue;
+          this.removeAllListeners(key);
+        }
+        this.removeAllListeners('removeListener');
+        this._events = Object.create(null);
+        this._eventsCount = 0;
+        return this;
+      }
+
+      listeners = events[type];
+
+      if (typeof listeners === 'function') {
+        this.removeListener(type, listeners);
+      } else if (listeners !== undefined) {
+        // LIFO order
+        for (i = listeners.length - 1; i >= 0; i--) {
+          this.removeListener(type, listeners[i]);
+        }
+      }
+
+      return this;
+    };
+
+function _listeners(target, type, unwrap) {
+  var events = target._events;
+
+  if (events === undefined)
+    return [];
+
+  var evlistener = events[type];
+  if (evlistener === undefined)
+    return [];
+
+  if (typeof evlistener === 'function')
+    return unwrap ? [evlistener.listener || evlistener] : [evlistener];
+
+  return unwrap ?
+    unwrapListeners(evlistener) : arrayClone(evlistener, evlistener.length);
+}
+
+EventEmitter.prototype.listeners = function listeners(type) {
+  return _listeners(this, type, true);
+};
+
+EventEmitter.prototype.rawListeners = function rawListeners(type) {
+  return _listeners(this, type, false);
+};
+
+EventEmitter.listenerCount = function(emitter, type) {
+  if (typeof emitter.listenerCount === 'function') {
+    return emitter.listenerCount(type);
+  } else {
+    return listenerCount.call(emitter, type);
+  }
+};
+
+EventEmitter.prototype.listenerCount = listenerCount;
+function listenerCount(type) {
+  var events = this._events;
+
+  if (events !== undefined) {
+    var evlistener = events[type];
+
+    if (typeof evlistener === 'function') {
+      return 1;
+    } else if (evlistener !== undefined) {
+      return evlistener.length;
+    }
+  }
+
+  return 0;
+}
+
+EventEmitter.prototype.eventNames = function eventNames() {
+  return this._eventsCount > 0 ? ReflectOwnKeys(this._events) : [];
+};
+
+function arrayClone(arr, n) {
+  var copy = new Array(n);
+  for (var i = 0; i < n; ++i)
+    copy[i] = arr[i];
+  return copy;
+}
+
+function spliceOne(list, index) {
+  for (; index + 1 < list.length; index++)
+    list[index] = list[index + 1];
+  list.pop();
+}
+
+function unwrapListeners(arr) {
+  var ret = new Array(arr.length);
+  for (var i = 0; i < ret.length; ++i) {
+    ret[i] = arr[i].listener || arr[i];
+  }
+  return ret;
+}
+
+export function once(emitter, name) {
+  return new Promise(function (resolve, reject) {
+    function errorListener(err) {
+      emitter.removeListener(name, resolver);
+      reject(err);
+    }
+
+    function resolver() {
+      if (typeof emitter.removeListener === 'function') {
+        emitter.removeListener('error', errorListener);
+      }
+      resolve([].slice.call(arguments));
+    };
+
+    eventTargetAgnosticAddListener(emitter, name, resolver, { once: true });
+    if (name !== 'error') {
+      addErrorHandlerIfEventEmitter(emitter, errorListener, { once: true });
+    }
+  });
+}
+
+function addErrorHandlerIfEventEmitter(emitter, handler, flags) {
+  if (typeof emitter.on === 'function') {
+    eventTargetAgnosticAddListener(emitter, 'error', handler, flags);
+  }
+}
+
+function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
+  if (typeof emitter.on === 'function') {
+    if (flags.once) {
+      emitter.once(name, listener);
+    } else {
+      emitter.on(name, listener);
+    }
+  } else if (typeof emitter.addEventListener === 'function') {
+    // EventTarget does not have `error` event semantics like Node
+    // EventEmitters, we do not listen for `error` events here.
+    emitter.addEventListener(name, function wrapListener(arg) {
+      // IE does not have builtin `{ once: true }` support so we
+      // have to do it manually.
+      if (flags.once) {
+        emitter.removeEventListener(name, wrapListener);
+      }
+      listener(arg);
+    });
+  } else {
+    throw new TypeError('The "emitter" argument must be of type EventEmitter. Received type ' + typeof emitter);
+  }
+}
diff --git a/package.json b/package.json
index 6d8c770..8d59814 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "events",
-  "version": "3.3.0",
+  "version": "3.3.1",
   "description": "Node's event emitter for all engines.",
   "keywords": [
     "events",
@@ -18,11 +18,13 @@
     "url": "http://github.com/browserify/events/issues/"
   },
   "main": "./events.js",
+  "module": "./events.mjs",
   "engines": {
     "node": ">=0.8.x"
   },
   "devDependencies": {
     "airtap": "^1.0.0",
+    "esbuild": "^0.14.49",
     "functions-have-names": "^1.2.1",
     "has": "^1.0.3",
     "has-symbols": "^1.0.1",
@@ -30,6 +32,7 @@
     "tape": "^5.0.0"
   },
   "scripts": {
+    "build": "esbuild events.mjs --platform=node --bundle --target=node0.8 --outfile=events.js",
     "test": "node tests/index.js",
     "test:browsers": "airtap -- tests/index.js"
   },