1 files changed, 41 insertions, 1 deletions
diff --git a/Timeline/ClientApp/src/app/common.ts b/Timeline/ClientApp/src/app/common.ts
index 0b11791a..56fdbc0e 100644
--- a/Timeline/ClientApp/src/app/common.ts
+++ b/Timeline/ClientApp/src/app/common.ts
@@ -1,4 +1,44 @@
+import React from 'react';
+import { Observable, Subject } from 'rxjs';
+
 // This error is thrown when ui goes wrong with bad logic.
-// Such as am variable should not be null, but it does.
+// Such as a variable should not be null, but it does.
 // This error should never occur. If it does, it indicates there is some logic bug in codes.
 export class UiLogicError extends Error {}
+
+export function useEventEmiiter(): [() => Observable<null>, () => void] {
+  const ref = React.useRef<Subject<null> | null>(null);
+
+  return React.useMemo(() => {
+    const getter = (): Subject<null> => {
+      if (ref.current == null) {
+        ref.current = new Subject<null>();
+      }
+      return ref.current;
+    };
+    const trigger = (): void => {
+      getter().next(null);
+    };
+    return [getter, trigger];
+  }, []);
+}
+
+export function useValueEventEmiiter<T>(): [
+  () => Observable<T>,
+  (value: T) => void
+] {
+  const ref = React.useRef<Subject<T> | null>(null);
+
+  return React.useMemo(() => {
+    const getter = (): Subject<T> => {
+      if (ref.current == null) {
+        ref.current = new Subject<T>();
+      }
+      return ref.current;
+    };
+    const trigger = (value: T): void => {
+      getter().next(value);
+    };
+    return [getter, trigger];
+  }, []);
+}