Have common only reference within common

Part of #1337

src/common/EventEmitter.ts

@@ -0,0 +1,85 @@
+/**
+ * Copyright (c) 2017 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { XtermListener } from './Types';
+import { IEventEmitter, IDisposable } from 'xterm';
+import { Disposable } from './Lifecycle';
+
+export class EventEmitter extends Disposable implements IEventEmitter, IDisposable {
+  private _events: {[type: string]: XtermListener[]};
+
+  constructor() {
+    super();
+    // Restore the previous events if available, this will happen if the
+    // constructor is called multiple times on the same object (terminal reset).
+    this._events = this._events || {};
+  }
+
+  public on(type: string, listener: XtermListener): void {
+    this._events[type] = this._events[type] || [];
+    this._events[type].push(listener);
+  }
+
+  /**
+   * Adds a disposabe listener to the EventEmitter, returning the disposable.
+   * @param type The event type.
+   * @param handler The handler for the listener.
+   */
+  public addDisposableListener(type: string, handler: XtermListener): IDisposable {
+    // TODO: Rename addDisposableEventListener to more easily disambiguate from Dom listener
+    this.on(type, handler);
+    return {
+      dispose: () => {
+        if (!handler) {
+          // Already disposed
+          return;
+        }
+        this.off(type, handler);
+        handler = null;
+      }
+    };
+  }
+
+  public off(type: string, listener: XtermListener): void {
+    if (!this._events[type]) {
+      return;
+    }
+
+    const obj = this._events[type];
+    let i = obj.length;
+
+    while (i--) {
+      if (obj[i] === listener) {
+        obj.splice(i, 1);
+        return;
+      }
+    }
+  }
+
+  public removeAllListeners(type: string): void {
+    if (this._events[type]) {
+       delete this._events[type];
+    }
+  }
+
+  public emit(type: string, ...args: any[]): void {
+    if (!this._events[type]) {
+      return;
+    }
+    const obj = this._events[type];
+    for (let i = 0; i < obj.length; i++) {
+      obj[i].apply(this, args);
+    }
+  }
+
+  public listeners(type: string): XtermListener[] {
+    return this._events[type] || [];
+  }
+
+  public dispose(): void {
+    super.dispose();
+    this._events = {};
+  }
+}