fix: subscribeOnce unsubscribe from undefined object

index.test.ts

@@ -236,3 +236,20 @@ it ('can release keeped handle', async () => {
   await sleep(5);
   expect(counter).to.equal(23);
 });
+
+it ('can compose keep and subscribeOnce', async () => {
+  const topic = new Topic<{
+    hello: (num: number) => void;
+  }>();
+
+  let counter = 0;
+
+  const token1 = topic.keep('hello', true, 1);
+  topic.subscribeOnce('hello', (num) => {
+    counter += num;
+  });
+
+  expect(counter).to.equal(1);
+
+  token1.release();
+});

index.ts

@@ -52,11 +52,21 @@ export class Topic<T extends CommonObject> {
   }
 
   subscribeOnce<K extends keyof T>(name: K, fn: Callback<T, K>): SubscribeToken {
+    let executed = false;
+
     const token = this.subscribe(name, function () {
       fn.apply(null, arguments as unknown as Parameters<T[K]>);
-      token.unsubscribe();
+      if (token) {
+        token.unsubscribe();
+      } else {
+        executed = true;
+      }
     });
 
+    if (executed) {
+      token.unsubscribe();
+    }
+
     return token;
   }
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "topic",
-  "version": "2.1.0",
+  "version": "2.1.2",
   "description": "subscribe and publish your business.",
   "main": "index.cjs.js",
   "module": "index.module.js",