1 files changed, 4 insertions, 0 deletions
diff --git a/Timeline/ClientApp/src/common.ts b/Timeline/ClientApp/src/common.ts
new file mode 100644
index 00000000..673f1c98
--- /dev/null
+++ b/Timeline/ClientApp/src/common.ts
@@ -0,0 +1,4 @@
+// This error is thrown when ui goes wrong with bad logic.
+// Such as am 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 {}