1 files changed, 42 insertions, 0 deletions
diff --git a/src/util/TypedEvent.ts b/src/util/TypedEvent.ts
new file mode 100644
index 000000000..0714a7f5c
--- /dev/null
+++ b/src/util/TypedEvent.ts
@@ -0,0 +1,42 @@
+export interface Listener<T> {
+  (event: T): any;
+}
+
+export interface Disposable {
+  dispose(): void;
+}
+
+/** passes through events as they happen. You will not get events from before you start listening */
+export class TypedEvent<T> {
+  private listeners: Listener<T>[] = [];
+  private listenersOncer: Listener<T>[] = [];
+
+  on = (listener: Listener<T>): Disposable => {
+    this.listeners.push(listener);
+    return {
+      dispose: () => this.off(listener)
+    };
+  }
+
+  once = (listener: Listener<T>): void => {
+    this.listenersOncer.push(listener);
+  }
+
+  off = (listener: Listener<T>) => {
+    var callbackIndex = this.listeners.indexOf(listener);
+    if (callbackIndex > -1) this.listeners.splice(callbackIndex, 1);
+  }
+
+  emit = (event: T) => {
+    /** Update any general listeners */
+    this.listeners.forEach((listener) => listener(event));
+
+    /** Clear the `once` queue */
+    this.listenersOncer.forEach((listener) => listener(event));
+    this.listenersOncer = [];
+  }
+
+  pipe = (te: TypedEvent<T>): Disposable => {
+    return this.on((e) => te.emit(e));
+  }
+}
+\ No newline at end of file