Convert EventEmitter to TS

Pat of #335

src/EventEmitter.ts

@@ -0,0 +1,80 @@
+/**
+ * @license MIT
+ */
+
+interface ListenerType {
+    (): void;
+    listener?: () => void;
+};
+
+export class EventEmitter {
+  private _events: {[type: string]: ListenerType[]};
+
+  constructor() {
+    this._events = this._events || {};
+  }
+
+  // TODO: Merge addListener and on, no reason for an alias in a private component
+  public addListener(type, listener): void {
+    this._events[type] = this._events[type] || [];
+    this._events[type].push(listener);
+  }
+
+  public on(type, listener): void {
+    this.addListener(type, listener);
+  }
+
+  // TODO: Merge removeListener and off, no reason for an alias in a private component
+  public removeListener(type, listener): void {
+    if (!this._events[type]) {
+      return;
+    }
+
+    let obj = this._events[type];
+    let i = obj.length;
+
+    while (i--) {
+      if (obj[i] === listener || obj[i].listener === listener) {
+        obj.splice(i, 1);
+        return;
+      }
+    }
+  }
+
+  public off(type, listener): void {
+    this.removeListener(type, listener);
+  }
+
+  public removeAllListeners(type): void {
+    if (this._events[type]) {
+       delete this._events[type];
+    }
+  }
+
+  public once(type, listener): any {
+    function on() {
+      let args = Array.prototype.slice.call(arguments);
+      this.removeListener(type, on);
+      return listener.apply(this, args);
+    }
+    (<any>on).listener = listener;
+    return this.on(type, on);
+  }
+
+  public emit(type): void {
+    if (!this._events[type]) {
+      return;
+    }
+
+    let args = Array.prototype.slice.call(arguments, 1);
+    let obj = this._events[type];
+
+    for (let i = 0; i < obj.length; i++) {
+      obj[i].apply(this, args);
+    }
+  }
+
+  public listeners(type): ListenerType[] {
+    return this._events[type] || [];
+  }
+}