Switch to use ESLint 10 (#5794)

frontend/src/core/components/pageEditor/hooks/usePageDocument.ts

@@ -217,7 +217,7 @@ export function usePageDocument(): PageDocumentHook {
     });
 
     // Build pages by interleaving original pages with insertions
-    let pages: PDFPage[] = [];
+    let pages: PDFPage[];
 
     // Helper function to create pages from a file (or placeholder if deselected)
     const createPagesFromFile = (fileId: FileId, startPageNumber: number, isSelected: boolean): PDFPage[] => {
@@ -242,11 +242,10 @@ export function usePageDocument(): PageDocumentHook {
       }
 
       const processedFile = stirlingFileStub.processedFile;
-      let filePages: PDFPage[] = [];
 
       if (processedFile?.pages && processedFile.pages.length > 0) {
         // Use fully processed pages with thumbnails
-        filePages = processedFile.pages.map((page, pageIndex) => ({
+        return processedFile.pages.map((page, pageIndex) => ({
           id: `${fileId}-${pageIndex + 1}`,
           pageNumber: startPageNumber + pageIndex,
           thumbnail: page.thumbnail || null,
@@ -259,9 +258,11 @@ export function usePageDocument(): PageDocumentHook {
           originalFileId: fileId,
           isPlaceholder: false,
         }));
-      } else if (processedFile?.totalPages) {
+      }
+
+      if (processedFile?.totalPages) {
         // Fallback: create pages without thumbnails but with correct count
-        filePages = Array.from({ length: processedFile.totalPages }, (_, pageIndex) => ({
+        return Array.from({ length: processedFile.totalPages }, (_, pageIndex) => ({
           id: `${fileId}-${pageIndex + 1}`,
           pageNumber: startPageNumber + pageIndex,
           originalPageNumber: pageIndex + 1,
@@ -272,23 +273,21 @@ export function usePageDocument(): PageDocumentHook {
           splitAfter: false,
           isPlaceholder: false,
         }));
-      } else {
-        // No processedFile yet - create a single loading placeholder
-        // This will be replaced when processing completes
-        filePages = [{
-          id: `${fileId}-loading`,
-          pageNumber: startPageNumber,
-          originalPageNumber: 1,
-          originalFileId: fileId,
-          rotation: 0,
-          thumbnail: null,
-          selected: false,
-          splitAfter: false,
-          isPlaceholder: true,
-        }];
       }
 
-      return filePages;
+      // No processedFile yet - create a single loading placeholder
+      // This will be replaced when processing completes
+      return [{
+        id: `${fileId}-loading`,
+        pageNumber: startPageNumber,
+        originalPageNumber: 1,
+        originalFileId: fileId,
+        rotation: 0,
+        thumbnail: null,
+        selected: false,
+        splitAfter: false,
+        isPlaceholder: true,
+      }];
     };
 
     // Collect all pages from original files, respecting their previous positions

frontend/src/core/components/shared/LocalIcon.tsx

@@ -4,13 +4,12 @@ import iconSet from '../../../assets/material-symbols-icons.json'; // eslint-dis
 
 // Load icons synchronously at import time - guaranteed to be ready on first render
 let iconsLoaded = false;
-let localIconCount = 0;
 
 try {
   if (iconSet) {
     addCollection(iconSet);
     iconsLoaded = true;
-    localIconCount = Object.keys(iconSet.icons || {}).length;
+    const localIconCount = Object.keys(iconSet.icons || {}).length;
     console.info(`✅ Local icons loaded: ${localIconCount} icons (${Math.round(JSON.stringify(iconSet).length / 1024)}KB)`);
   }
 } catch {

frontend/src/core/components/tools/addStamp/StampPreviewUtils.ts

@@ -110,7 +110,7 @@ export function computeStampPreviewStyle(
       // Convert measured px width back to PDF points using horizontal scale
       widthPtsContent = measuredWidthPx / scaleX;
 
-      let adjustmentFactor = 1.0;
+      let adjustmentFactor: number;
       switch (parameters.alphabet) {
         case 'roman':
           adjustmentFactor = 0.90;
@@ -126,6 +126,7 @@ export function computeStampPreviewStyle(
           break;
         default:
           adjustmentFactor = 0.93;
+          break;
       }
       widthPtsContent *= adjustmentFactor;
     }

frontend/src/core/components/tools/fullscreen/CompactToolItem.tsx

@@ -22,7 +22,7 @@ const CompactToolItem: React.FC<CompactToolItemProps> = ({ id, tool, isSelected,
   const iconBg = getIconBackground(categoryColor, false);
   const iconClasses = 'tool-panel__fullscreen-list-icon';
 
-  let iconNode: React.ReactNode = null;
+  let iconNode: React.ReactNode;
   if (React.isValidElement<{ style?: React.CSSProperties }>(tool.icon)) {
     const element = tool.icon as React.ReactElement<{ style?: React.CSSProperties }>;
     iconNode = React.cloneElement(element, {
@@ -120,4 +120,3 @@ const CompactToolItem: React.FC<CompactToolItemProps> = ({ id, tool, isSelected,
 
 export default CompactToolItem;
 
-

frontend/src/core/components/tools/fullscreen/DetailedToolItem.tsx

@@ -21,7 +21,7 @@ const DetailedToolItem: React.FC<DetailedToolItemProps> = ({ id, tool, isSelecte
   const iconBg = getIconBackground(categoryColor, true);
   const iconClasses = 'tool-panel__fullscreen-icon';
 
-  let iconNode: React.ReactNode = null;
+  let iconNode: React.ReactNode;
   if (React.isValidElement<{ style?: React.CSSProperties }>(tool.icon)) {
     const element = tool.icon as React.ReactElement<{ style?: React.CSSProperties }>;
     iconNode = React.cloneElement(element, {
@@ -70,7 +70,7 @@ const DetailedToolItem: React.FC<DetailedToolItemProps> = ({ id, tool, isSelecte
               color="orange"
             >
               {/* we can add more translations for different badges in future, like beta, etc. */}
-            {t('toolPanel.alpha', 'Alpha')} 
+            {t('toolPanel.alpha', 'Alpha')}
             </Badge>
           )}
         </div>
@@ -106,4 +106,3 @@ const DetailedToolItem: React.FC<DetailedToolItemProps> = ({ id, tool, isSelecte
 
 export default DetailedToolItem;
 
-

frontend/src/core/hooks/tools/convert/useConvertParameters.ts

@@ -133,7 +133,7 @@ const validateParameters = (params: ConvertParameters): boolean => {
   if (!fromExtension || !toExtension) return false;
 
   // Handle dynamic format identifiers (file-<extension>)
-  let supportedToExtensions: string[] = [];
+  let supportedToExtensions: string[];
   if (fromExtension.startsWith('file-')) {
     // Dynamic format - use 'any' conversion options
     supportedToExtensions = CONVERSION_MATRIX['any'] || [];

frontend/src/core/hooks/tools/removeAnnotations/useRemoveAnnotationsOperation.ts

@@ -71,7 +71,10 @@ const removeAnnotationsProcessor = async (_parameters: RemoveAnnotationsParamete
       processedFiles.push(processedFile);
     } catch (error) {
       console.error('Error processing file:', file.name, error);
-      throw new Error(`Failed to process ${file.name}: ${error instanceof Error ? error.message : 'Unknown error'}`);
+      throw new Error(
+        `Failed to process ${file.name}: ${error instanceof Error ? error.message : 'Unknown error'}`,
+        { cause: error }
+      );
     }
   }
 
@@ -96,4 +99,4 @@ export const useRemoveAnnotationsOperation = () => {
     ...removeAnnotationsOperationConfig,
     getErrorMessage: createStandardErrorHandler(t('removeAnnotations.error.failed', 'An error occurred while removing annotations from the PDF.'))
   });
-};
+};

frontend/src/core/hooks/tools/shared/useToolApiCalls.ts

@@ -77,7 +77,7 @@ export const useToolApiCalls = <TParams = void>() => {
 
       } catch (error) {
         if (axios.isCancel(error)) {
-          throw new Error('Operation was cancelled');
+          throw new Error('Operation was cancelled', { cause: error });
         }
         console.error('[processFiles] Failed', { name: file.name, error });
         failedFiles.push(file.name);

frontend/src/core/hooks/tools/validateSignature/signatureReportPdf.ts

@@ -71,7 +71,7 @@ export const createReportPdf = async (
     cursorY -= 16;
 
     if (entry.error) {
-      cursorY = drawCenteredMessage({
+      drawCenteredMessage({
         page,
         font,
         fontBold,
@@ -86,7 +86,7 @@ export const createReportPdf = async (
     }
 
     if (entry.signatures.length === 0) {
-      cursorY = drawCenteredMessage({
+      drawCenteredMessage({
         page,
         font,
         fontBold,

frontend/src/core/hooks/useCookieConsent.ts

@@ -71,8 +71,7 @@ export const useCookieConsent = ({
           const hasDarkClass = document.documentElement.classList.contains('dark');
           const systemPrefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
 
-          let isDarkMode = false;
-
+          let isDarkMode: boolean;
           if (mantineScheme) {
             isDarkMode = mantineScheme === 'dark';
           } else if (hasLightClass) {
@@ -94,9 +93,8 @@ export const useCookieConsent = ({
           return;
         }
 
-        let themeObserver: MutationObserver | null = null;
         if (!forceLightMode) {
-          themeObserver = new MutationObserver((mutations) => {
+          const themeObserver = new MutationObserver((mutations) => {
             mutations.forEach((mutation) => {
               if (mutation.type === 'attributes' &&
                   (mutation.attributeName === 'data-mantine-color-scheme' ||
@@ -241,7 +239,7 @@ export const useCookieConsent = ({
       const hasDarkClass = document.documentElement.classList.contains('dark');
       const systemPrefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
 
-      let isDarkMode = false;
+      let isDarkMode: boolean;
       if (mantineScheme) {
         isDarkMode = mantineScheme === 'dark';
       } else if (hasLightClass) {

frontend/src/core/services/fileStorage.ts

@@ -335,10 +335,10 @@ class FileStorageService {
    * Get storage statistics
    */
   async getStorageStats(): Promise<StorageStats> {
-    let used = 0;
+    let used: number;
+    let fileCount: number;
     let available = 0;
     let quota: number | undefined;
-    let fileCount = 0;
 
     try {
       // Get browser quota for context

frontend/src/core/services/pdfExportService.ts

@@ -37,7 +37,10 @@ export class PDFExportService {
       return { blob, filename: exportFilename };
     } catch (error) {
       console.error('PDF export error:', error);
-      throw new Error(`Failed to export PDF: ${error instanceof Error ? error.message : 'Unknown error'}`);
+      throw new Error(
+        `Failed to export PDF: ${error instanceof Error ? error.message : 'Unknown error'}`,
+        { cause: error }
+      );
     }
   }
 
@@ -68,7 +71,10 @@ export class PDFExportService {
       return { blob, filename: exportFilename };
     } catch (error) {
       console.error('Multi-file PDF export error:', error);
-      throw new Error(`Failed to export PDF: ${error instanceof Error ? error.message : 'Unknown error'}`);
+      throw new Error(
+        `Failed to export PDF: ${error instanceof Error ? error.message : 'Unknown error'}`,
+        { cause: error }
+      );
     }
   }
 

frontend/src/core/services/zipFileService.ts

@@ -162,7 +162,10 @@ export class ZipFileService {
 
       return { zipFile, size: zipFile.size };
     } catch (error) {
-      throw new Error(`Failed to create ZIP file: ${error instanceof Error ? error.message : 'Unknown error'}`);
+      throw new Error(
+        `Failed to create ZIP file: ${error instanceof Error ? error.message : 'Unknown error'}`,
+        { cause: error }
+      );
     }
   }
 

frontend/src/core/tools/pdfTextEditor/PdfTextEditor.tsx

@@ -687,7 +687,7 @@ const PdfTextEditor = ({ onComplete, onError }: BaseToolProps) => {
                 message: pollError?.message,
               });
               if (pollError?.response?.status === 404) {
-                throw new Error('Job not found on server');
+                throw new Error('Job not found on server', { cause: pollError });
               }
             }
           }
@@ -1164,7 +1164,9 @@ const PdfTextEditor = ({ onComplete, onError }: BaseToolProps) => {
           return;
         } catch (incrementalError) {
           if (isLazyMode && cachedJobIdRef.current) {
-            throw new Error('Incremental export failed for cached document. Please reload and retry.');
+            throw new Error('Incremental export failed for cached document. Please reload and retry.', {
+              cause: incrementalError,
+            });
           }
           console.warn(
             '[handleGeneratePdf] Incremental export failed, falling back to full export',
@@ -1340,7 +1342,9 @@ const PdfTextEditor = ({ onComplete, onError }: BaseToolProps) => {
           pdfBlob = response.data;
         } catch (incrementalError) {
           if (isLazyMode && cachedJobId) {
-            throw new Error('Incremental export failed for cached document. Please reload and retry.');
+            throw new Error('Incremental export failed for cached document. Please reload and retry.', {
+              cause: incrementalError,
+            });
           }
           console.warn(
             '[handleSaveToWorkbench] Incremental export failed, falling back to full export',
@@ -1354,7 +1358,7 @@ const PdfTextEditor = ({ onComplete, onError }: BaseToolProps) => {
 
           const payload = buildPayload();
           if (!payload) {
-            throw new Error('Failed to build payload');
+            throw new Error('Failed to build payload', { cause: incrementalError });
           }
 
           const { document, filename } = payload;

frontend/src/core/utils/automationExecutor.ts

@@ -174,7 +174,9 @@ export const executeToolOperationWithPrefix = async (
 
   } catch (error: any) {
     console.error(`❌ ${operationName} failed:`, error);
-    throw new Error(`${operationName} operation failed: ${error.response?.data || error.message}`);
+    throw new Error(`${operationName} operation failed: ${error.response?.data || error.message}`, {
+      cause: error,
+    });
   }
 };
 

frontend/src/core/utils/imageToPdfUtils.ts

@@ -139,7 +139,8 @@ export async function convertImageToPdf(
   } catch (error) {
     console.error('Error converting image to PDF:', error);
     throw new Error(
-      `Failed to convert image to PDF: ${error instanceof Error ? error.message : 'Unknown error'}`
+      `Failed to convert image to PDF: ${error instanceof Error ? error.message : 'Unknown error'}`,
+      { cause: error }
     );
   }
 }

frontend/src/core/workers/compareWorker.ts

@@ -167,10 +167,10 @@ const chunkedDiff = (
     const remaining2 = Math.max(0, words2.length - index2);
 
     let windowSize = Math.max(dynamicChunkSize, buffer1.length, buffer2.length);
-    let window1: string[] = [];
-    let window2: string[] = [];
-    let chunkTokens: CompareDiffToken[] = [];
-    let reachedEnd = false;
+    let window1: string[];
+    let window2: string[];
+    let chunkTokens: CompareDiffToken[];
+    let reachedEnd: boolean;
 
     while (true) {
       const take1 = Math.min(Math.max(0, windowSize - buffer1.length), remaining1);
@@ -220,7 +220,6 @@ const chunkedDiff = (
         flushRemainder();
         return;
       }
-      windowSize = Math.min(windowSize + dynamicStep, dynamicMaxWindow);
       stallIterations += 1;
       if (stallIterations >= 3) {
         increaseChunkSizes();
@@ -422,7 +421,7 @@ self.onmessage = (event: MessageEvent<CompareWorkerRequest>) => {
       },
       { maxProcessedTokens: runtimeMaxProcessedTokens, minUnchangedRatio: runtimeMinUnchangedRatio }
     );
-  } catch (err) { 
+  } catch (err) {
     const error = err as Error & { __earlyStop?: boolean };
     if (error && (error.__earlyStop || error.message === 'EARLY_STOP_TOO_DISSIMILAR')) {
       const response: CompareWorkerResponse = {

frontend/src/desktop/services/authService.ts

@@ -247,9 +247,9 @@ export class AuthService {
           error.response?.data?.msg ||
           error.response?.data?.message ||
           error.message;
-        throw new Error(message || 'Sign up failed');
+        throw new Error(message || 'Sign up failed', { cause: error });
       }
-      throw error instanceof Error ? error : new Error('Sign up failed');
+      throw error instanceof Error ? error : new Error('Sign up failed', { cause: error });
     }
   }
 
@@ -282,7 +282,7 @@ export class AuthService {
         await this.saveTokenEverywhere(token);
       } catch (error) {
         console.error('[Desktop AuthService] Failed to save token:', error);
-        throw new Error('Failed to save authentication token');
+        throw new Error('Failed to save authentication token', { cause: error });
       }
 
       // Save user info to store
@@ -320,37 +320,49 @@ export class AuthService {
         // Authentication errors
         if (errMsg.includes('401') || errMsg.includes('unauthorized') || errMsg.includes('invalid credentials')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Invalid username or password. Please check your credentials and try again.');
+          throw new Error('Invalid username or password. Please check your credentials and try again.', {
+            cause: error,
+          });
         }
         // Server not found or unreachable
         else if (errMsg.includes('connection refused') || errMsg.includes('econnrefused')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Cannot connect to server. Please check the server URL and ensure the server is running.');
+          throw new Error('Cannot connect to server. Please check the server URL and ensure the server is running.', {
+            cause: error,
+          });
         }
         // Timeout
         else if (errMsg.includes('timeout') || errMsg.includes('timed out')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Login request timed out. Please check your network connection and try again.');
+          throw new Error('Login request timed out. Please check your network connection and try again.', {
+            cause: error,
+          });
         }
         // DNS failure
         else if (errMsg.includes('getaddrinfo') || errMsg.includes('dns') || errMsg.includes('not found') || errMsg.includes('enotfound')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Cannot resolve server address. Please check the server URL is correct.');
+          throw new Error('Cannot resolve server address. Please check the server URL is correct.', { cause: error });
         }
         // SSL/TLS errors
         else if (errMsg.includes('ssl') || errMsg.includes('tls') || errMsg.includes('certificate') || errMsg.includes('cert')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('SSL/TLS certificate error. Server may have an invalid or self-signed certificate.');
+          throw new Error('SSL/TLS certificate error. Server may have an invalid or self-signed certificate.', {
+            cause: error,
+          });
         }
         // 404 - endpoint not found
         else if (errMsg.includes('404') || errMsg.includes('not found')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Login endpoint not found. Please ensure you are connecting to a valid Stirling PDF server.');
+          throw new Error('Login endpoint not found. Please ensure you are connecting to a valid Stirling PDF server.', {
+            cause: error,
+          });
         }
         // 403 - security disabled
         else if (errMsg.includes('403') || errMsg.includes('forbidden')) {
           this.setAuthStatus('unauthenticated', null);
-          throw new Error('Login is not enabled on this server. Please enable security mode (DOCKER_ENABLE_SECURITY=true).');
+          throw new Error('Login is not enabled on this server. Please enable security mode (DOCKER_ENABLE_SECURITY=true).', {
+            cause: error,
+          });
         }
       }