Better is abortable checker

src/index.ts

@@ -35,7 +35,7 @@ export default class AbortablePromise<T> implements Promise<T | null> {
       on_abort?: () => Promise<unknown> | void
     ): Promise<L | null> {
       console.log("await_or_abort", promise);
-      if (promise instanceof AbortablePromise && !on_abort) {
+      if (AbortablePromise.isAbortable(promise) && !on_abort) {
         on_abort = async () => promise.abort();
       }
       if (on_abort === undefined) {
@@ -82,6 +82,10 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     this.emitter = emitter;
   }
 
+  static isAbortable(o: unknown): o is AbortablePromise<unknown> {
+    return (o as { abort: boolean }).abort;
+  }
+
   abort() {
     this.emitter.abort();
   }