feat: add ESM version

Related: socketio/socket.io-client#1536

index.mjs

@@ -0,0 +1,169 @@
+/**
+ * Initialize a new `Emitter`.
+ *
+ * @api public
+ */
+
+export function Emitter(obj) {
+  if (obj) return mixin(obj);
+}
+
+/**
+ * Mixin the emitter properties.
+ *
+ * @param {Object} obj
+ * @return {Object}
+ * @api private
+ */
+
+function mixin(obj) {
+  for (var key in Emitter.prototype) {
+    obj[key] = Emitter.prototype[key];
+  }
+  return obj;
+}
+
+/**
+ * Listen on the given `event` with `fn`.
+ *
+ * @param {String} event
+ * @param {Function} fn
+ * @return {Emitter}
+ * @api public
+ */
+
+Emitter.prototype.on =
+Emitter.prototype.addEventListener = function(event, fn){
+  this._callbacks = this._callbacks || {};
+  (this._callbacks['$' + event] = this._callbacks['$' + event] || [])
+    .push(fn);
+  return this;
+};
+
+/**
+ * Adds an `event` listener that will be invoked a single
+ * time then automatically removed.
+ *
+ * @param {String} event
+ * @param {Function} fn
+ * @return {Emitter}
+ * @api public
+ */
+
+Emitter.prototype.once = function(event, fn){
+  function on() {
+    this.off(event, on);
+    fn.apply(this, arguments);
+  }
+
+  on.fn = fn;
+  this.on(event, on);
+  return this;
+};
+
+/**
+ * Remove the given callback for `event` or all
+ * registered callbacks.
+ *
+ * @param {String} event
+ * @param {Function} fn
+ * @return {Emitter}
+ * @api public
+ */
+
+Emitter.prototype.off =
+Emitter.prototype.removeListener =
+Emitter.prototype.removeAllListeners =
+Emitter.prototype.removeEventListener = function(event, fn){
+  this._callbacks = this._callbacks || {};
+
+  // all
+  if (0 == arguments.length) {
+    this._callbacks = {};
+    return this;
+  }
+
+  // specific event
+  var callbacks = this._callbacks['$' + event];
+  if (!callbacks) return this;
+
+  // remove all handlers
+  if (1 == arguments.length) {
+    delete this._callbacks['$' + event];
+    return this;
+  }
+
+  // remove specific handler
+  var cb;
+  for (var i = 0; i < callbacks.length; i++) {
+    cb = callbacks[i];
+    if (cb === fn || cb.fn === fn) {
+      callbacks.splice(i, 1);
+      break;
+    }
+  }
+
+  // Remove event specific arrays for event types that no
+  // one is subscribed for to avoid memory leak.
+  if (callbacks.length === 0) {
+    delete this._callbacks['$' + event];
+  }
+
+  return this;
+};
+
+/**
+ * Emit `event` with the given args.
+ *
+ * @param {String} event
+ * @param {Mixed} ...
+ * @return {Emitter}
+ */
+
+Emitter.prototype.emit = function(event){
+  this._callbacks = this._callbacks || {};
+
+  var args = new Array(arguments.length - 1)
+    , callbacks = this._callbacks['$' + event];
+
+  for (var i = 1; i < arguments.length; i++) {
+    args[i - 1] = arguments[i];
+  }
+
+  if (callbacks) {
+    callbacks = callbacks.slice(0);
+    for (var i = 0, len = callbacks.length; i < len; ++i) {
+      callbacks[i].apply(this, args);
+    }
+  }
+
+  return this;
+};
+
+// alias used for reserved events (protected method)
+Emitter.prototype.emitReserved = Emitter.prototype.emit;
+
+/**
+ * Return array of callbacks for `event`.
+ *
+ * @param {String} event
+ * @return {Array}
+ * @api public
+ */
+
+Emitter.prototype.listeners = function(event){
+  this._callbacks = this._callbacks || {};
+  return this._callbacks['$' + event] || [];
+};
+
+/**
+ * Check if this emitter has `event` handlers.
+ *
+ * @param {String} event
+ * @return {Boolean}
+ * @api public
+ */
+
+Emitter.prototype.hasListeners = function(event){
+  return !! this.listeners(event).length;
+};

package.json

@@ -13,6 +13,7 @@
     }
   },
   "main": "index.js",
+  "module": "index.mjs",
   "types": "index.d.ts",
   "repository": {
     "type": "git",
@@ -23,6 +24,7 @@
   },
   "files": [
     "index.js",
+    "index.mjs",
     "index.d.ts",
     "LICENSE"
   ]