Initialize all widget-related things at the top level

src/LazyEventEmitter.ts

@@ -0,0 +1,90 @@
+/*
+Copyright 2022 Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import EventEmitter from "events";
+
+type NonEmptyArray<T> = [T, ...T[]];
+
+/**
+ * An event emitter that lets events pile up in a backlog until a listener is
+ * present, at which point any events that were missed are re-emitted.
+ */
+export class LazyEventEmitter extends EventEmitter {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  private eventBacklogs = new Map<string | symbol, NonEmptyArray<any[]>>();
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  public emit(type: string | symbol, ...args: any[]): boolean {
+    const hasListeners = super.emit(type, ...args);
+
+    if (!hasListeners) {
+      // The event was missed, so add it to the backlog
+      const backlog = this.eventBacklogs.get(type);
+      if (backlog) {
+        backlog.push(args);
+      } else {
+        // Start a new backlog
+        this.eventBacklogs.set(type, [args]);
+      }
+    }
+
+    return hasListeners;
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  public on(type: string | symbol, listener: (...args: any[]) => void): this {
+    super.on(type, listener);
+
+    const backlog = this.eventBacklogs.get(type);
+    if (backlog) {
+      // That was the first listener for this type, so let's send it all the
+      // events that have piled up
+      for (const args of backlog) super.emit(type, ...args);
+      // Backlog is now clear
+      this.eventBacklogs.delete(type);
+    }
+
+    return this;
+  }
+
+  public addListener(
+    type: string | symbol,
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    listener: (...args: any[]) => void
+  ): this {
+    return this.on(type, listener);
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  public once(type: string | symbol, listener: (...args: any[]) => void): this {
+    super.once(type, listener);
+
+    const backlog = this.eventBacklogs.get(type);
+    if (backlog) {
+      // That was the first listener for this type, so let's send it the first
+      // of the events that have piled up
+      super.emit(type, ...backlog[0]);
+      // Clear the event from the backlog
+      if (backlog.length === 1) {
+        this.eventBacklogs.delete(type);
+      } else {
+        backlog.shift();
+      }
+    }
+
+    return this;
+  }
+}