fix: addDisposableDomListener dispose() leaking

src/browser/Lifecycle.test.ts

@@ -0,0 +1,40 @@
+/**
+ * Copyright (c) 2020 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { assert } from 'chai';
+import { addDisposableDomListener } from './Lifecycle';
+import jsdom = require('jsdom');
+
+describe('addDisposableDomListener', () => {
+  const dom = new jsdom.JSDOM();
+  const document = dom.window.document;
+
+  function createEvent(type: string): Event {
+    const event = document.createEvent('Event');
+    event.initEvent(type);
+    return event;
+  }
+
+  it('dispose', () => {
+    let calledTimes = 0;
+    const div = document.createElement('div');
+    const disposable = addDisposableDomListener(div, 'test', () => { calledTimes++; });
+
+    assert.equal(calledTimes, 0);
+
+    div.dispatchEvent(createEvent('test'));
+    assert.equal(calledTimes, 1);
+
+    disposable.dispose();
+
+    div.dispatchEvent(createEvent('test'));
+    assert.equal(calledTimes, 1);
+
+    disposable.dispose(); // double disposing
+
+    div.dispatchEvent(createEvent('test'));
+    assert.equal(calledTimes, 1);
+  });
+});

src/browser/Lifecycle.ts

@@ -20,7 +20,7 @@ export function addDisposableDomListener(
   let disposed = false;
   return {
     dispose: () => {
-      if (!disposed) {
+      if (disposed) {
         return;
       }
       disposed = true;