Merge front end repo

1 files changed, 44 insertions, 0 deletions

diff --git a/Timeline/ClientApp/src/app/common.ts b/Timeline/ClientApp/src/app/common.ts
new file mode 100644
index 00000000..297b4a77
--- /dev/null
+++ b/Timeline/ClientApp/src/app/common.ts
@@ -0,0 +1,44 @@
+import React from 'react';

+import { Observable, Subject } from 'rxjs';

+

+// This error is thrown when ui goes wrong with bad logic.

+// 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];

+  }, []);

+}