diff --git a/client/src/pages/History.tsx b/client/src/pages/History.tsx
index aaea3da4..c8ce9546 100644
--- a/client/src/pages/History.tsx
+++ b/client/src/pages/History.tsx
@@ -277,7 +277,8 @@ export default function History() {
         method: "POST",
         body: formData
       });
-      const data = await response.json();
+      if (!response.ok) throw new Error("Request failed");
+const data = await response.json();
       toast({ title: "Success", description: data.message });
     } catch (err: unknown) {
       toast({ title: "Upload Error", description: err instanceof Error ? (err as Error).message : String(err), variant: "destructive" });
diff --git a/server/controllers/assessments.controller.ts b/server/controllers/assessments.controller.ts
index abb342c6..0263b595 100644
--- a/server/controllers/assessments.controller.ts
+++ b/server/controllers/assessments.controller.ts
@@ -480,7 +480,7 @@ export const getAssessmentById = async (req: Request, res: Response) => {
   try {
     const id = parseInt(req.params.id as string, 10);
 
-    if (isNaN(id) || id <= 0) {
+    if (Number.isNaN(id) || id <= 0) {
       return res.status(400).json({ message: "Invalid assessment ID." });
     }
 
@@ -520,7 +520,7 @@ export const deleteAssessment = async (req: Request, res: Response) => {
   try {
     const id = parseInt(req.params.id as string, 10);
 
-    if (isNaN(id) || id <= 0) {
+    if (Number.isNaN(id) || id <= 0) {
       return res.status(400).json({ message: "Invalid assessment ID." });
     }
 
diff --git a/server/middleware/requireAssessmentAccess.ts b/server/middleware/requireAssessmentAccess.ts
index c8e23336..2674d0b5 100644
--- a/server/middleware/requireAssessmentAccess.ts
+++ b/server/middleware/requireAssessmentAccess.ts
@@ -20,7 +20,7 @@ export async function requireAssessmentAccess(
   try {
     const id = parseInt(req.params.id as string, 10);
 
-    if (isNaN(id) || id <= 0) {
+    if (Number.isNaN(id) || id <= 0) {
       return res.status(400).json({ message: "Invalid assessment ID." });
     }
 
diff --git a/server/repositories/assessment.repository.ts b/server/repositories/assessment.repository.ts
index ce85a8f5..ef1c8f94 100644
--- a/server/repositories/assessment.repository.ts
+++ b/server/repositories/assessment.repository.ts
@@ -147,12 +147,12 @@ export class AssessmentRepository {
       filters.push(lte(assessments.age, maxAge));
     }
 
-    if (startDate && !isNaN(Date.parse(startDate))) {
+    if (startDate && !Number.isNaN(Date.parse(startDate))) {
       const parsedStart = parseDateFilter(startDate);
       if (parsedStart) filters.push(gte(assessments.createdAt, parsedStart));
     }
 
-    if (endDate && !isNaN(Date.parse(endDate))) {
+    if (endDate && !Number.isNaN(Date.parse(endDate))) {
       const parsedEnd = parseDateFilter(endDate);
       if (parsedEnd) {
         parsedEnd.setUTCHours(23, 59, 59, 999);
@@ -451,11 +451,11 @@ export class AssessmentRepository {
     if (createdBy) {
       filters.push(eq(assessments.createdBy, createdBy));
     }
-    if (startDate && !isNaN(Date.parse(startDate))) {
+    if (startDate && !Number.isNaN(Date.parse(startDate))) {
       const parsedStart = parseDateFilter(startDate);
       if (parsedStart) filters.push(gte(assessments.createdAt, parsedStart));
     }
-    if (endDate && !isNaN(Date.parse(endDate))) {
+    if (endDate && !Number.isNaN(Date.parse(endDate))) {
       const parsedEnd = parseDateFilter(endDate);
       if (parsedEnd) {
         parsedEnd.setUTCHours(23, 59, 59, 999);
@@ -600,11 +600,11 @@ export class AssessmentRepository {
     if (params.maxHba1c !== undefined) filters.push(lte(assessments.hba1cLevel, params.maxHba1c));
     if (params.minGlucose !== undefined) filters.push(gte(assessments.bloodGlucoseLevel, params.minGlucose));
     if (params.maxGlucose !== undefined) filters.push(lte(assessments.bloodGlucoseLevel, params.maxGlucose));
-    if (params.startDate && !isNaN(Date.parse(params.startDate))) {
+    if (params.startDate && !Number.isNaN(Date.parse(params.startDate))) {
       const parsedStart = parseDateFilter(params.startDate);
       if (parsedStart) filters.push(gte(assessments.createdAt, parsedStart));
     }
-    if (params.endDate && !isNaN(Date.parse(params.endDate))) {
+    if (params.endDate && !Number.isNaN(Date.parse(params.endDate))) {
       const parsedEnd = parseDateFilter(params.endDate);
       if (parsedEnd) {
         parsedEnd.setUTCHours(23, 59, 59, 999);
diff --git a/server/utils/csvSanitizer.ts b/server/utils/csvSanitizer.ts
index ea861c81..7703446d 100644
--- a/server/utils/csvSanitizer.ts
+++ b/server/utils/csvSanitizer.ts
@@ -43,7 +43,7 @@ export function sanitizeCsvCell(value: unknown): string {
   }
 
   const trimmed = text.trim();
-  if (trimmed !== "" && !isNaN(Number(trimmed))) {
+  if (trimmed !== "" && !Number.isNaN(Number(trimmed))) {
     return text;
   }