diff --git a/optuna_dashboard/ts/components/GraphHistory.tsx b/optuna_dashboard/ts/components/GraphHistory.tsx
index a2b58c14..0afcb555 100644
--- a/optuna_dashboard/ts/components/GraphHistory.tsx
+++ b/optuna_dashboard/ts/components/GraphHistory.tsx
@@ -72,9 +72,9 @@ export const GraphHistory: FC<{
       markerSize
     )
     const element = document.getElementById(plotDomId)
-    if (element != null && studies.length >= 1) {
+    if (element !== null && studies.length >= 1) {
       // @ts-ignore
-      element.on("plotly_click", function (data) {
+      element.on("plotly_click", (data) => {
         if (data.points[0].data.mode !== "lines") {
           let studyId = 1
           if (data.points[0].data.name.includes("Infeasible Trial of")) {
diff --git a/optuna_dashboard/ts/components/GraphParetoFront.tsx b/optuna_dashboard/ts/components/GraphParetoFront.tsx
index d8911fd2..f2b11145 100644
--- a/optuna_dashboard/ts/components/GraphParetoFront.tsx
+++ b/optuna_dashboard/ts/components/GraphParetoFront.tsx
@@ -40,7 +40,7 @@ export const GraphParetoFront: FC<{
       const element = document.getElementById(plotDomId)
       if (element != null) {
         // @ts-ignore
-        element.on("plotly_click", function (data) {
+        element.on("plotly_click", (data) => {
           const plotTextInfo = JSON.parse(
             data.points[0].text.replace(/<br>/g, "")
           )