1 files changed, 60 insertions, 0 deletions
diff --git a/js/custom_event.ts b/js/custom_event.ts
new file mode 100644
index 000000000..dd1c33d58
--- /dev/null
+++ b/js/custom_event.ts
@@ -0,0 +1,60 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as domTypes from "./dom_types";
+import * as event from "./event";
+import { getPrivateValue } from "./util";
+
+// WeakMaps are recommended for private attributes (see MDN link below)
+// tslint:disable-next-line:max-line-length
+// https://developer.mozilla.org/en-US/docs/Archive/Add-ons/Add-on_SDK/Guides/Contributor_s_Guide/Private_Properties#Using_WeakMaps
+export const customEventAttributes = new WeakMap();
+
+export class CustomEventInit extends event.EventInit
+  implements domTypes.CustomEventInit {
+  // tslint:disable-next-line:no-any
+  detail: any;
+
+  constructor({
+    bubbles = false,
+    cancelable = false,
+    composed = false,
+    detail = null
+  }: domTypes.CustomEventInit) {
+    super({ bubbles, cancelable, composed });
+    this.detail = detail;
+  }
+}
+
+export class CustomEvent extends event.Event implements domTypes.CustomEvent {
+  constructor(
+    type: string,
+    customEventInitDict: domTypes.CustomEventInit = {}
+  ) {
+    super(type, customEventInitDict);
+    const { detail = null } = customEventInitDict;
+    customEventAttributes.set(this, { detail });
+  }
+
+  // tslint:disable-next-line:no-any
+  get detail(): any {
+    return getPrivateValue(this, customEventAttributes, "detail");
+  }
+
+  initCustomEvent(
+    type: string,
+    bubbles?: boolean,
+    cancelable?: boolean,
+    // tslint:disable-next-line:no-any
+    detail?: any
+  ) {
+    if (this.dispatched) {
+      return;
+    }
+
+    customEventAttributes.set(this, { detail });
+  }
+}
+
+/** Built-in objects providing `get` methods for our
+ * interceptable JavaScript operations.
+ */
+Reflect.defineProperty(CustomEvent.prototype, "detail", { enumerable: true });