refactor(frontend): improve type safety and migrate to ESLint 9

Migrate the frontend to ESLint 9, add `eslint.config.mjs`, and replace various `any` types with more specific or safer alternatives across the codebase.

- Update `package.json` with new ESLint and TypeScript-ESLint dependencies
- Replace `any` with `Record<string, unknown>` or specific types in `TemplatePicker`, `Editor`, and `FileBrowser`
- Improve error handling in `TeamSettings` and `Templates` using type guards
- Add explicit type imports for Excalidraw elements in `Editor.tsx`
- Refactor `Modal.tsx` for cleaner conditional logic
- Add `check` script to `package.json` for type checking

frontend/eslint.config.mjs

@@ -0,0 +1,19 @@
+import tseslint from 'typescript-eslint';
+import pluginReact from 'eslint-plugin-react';
+
+export default tseslint.config(
+  { ignores: ['dist/', 'node_modules/', 'dist-test/', '*.config.*', 'eslint.config.mjs', 'e2e/', 'playwright/'] },
+  tseslint.configs.recommended,
+  {
+    files: ['**/*.{ts,tsx}'],
+    plugins: { react: pluginReact },
+    languageOptions: {
+      parserOptions: { project: './tsconfig.json' },
+    },
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/no-non-null-assertion': 'warn',
+      'react/react-in-jsx-scope': 'off',
+    },
+  }
+);

frontend/package.json

@@ -6,8 +6,9 @@
   "scripts": {
     "dev": "vite",
     "build": "tsc && vite build",
+    "check": "tsc --noEmit",
     "preview": "vite preview",
-    "lint": "eslint . --ext ts,tsx --report-unused-disable-directives --max-warnings 0",
+    "lint": "eslint .",
     "typecheck": "tsc --noEmit",
     "test": "vitest",
     "test:ui": "vitest --ui",
@@ -37,9 +38,12 @@
     "@types/react": "^18.3.18",
     "@types/react-dom": "^18.3.5",
     "@vitejs/plugin-react": "^4.3.0",
+    "eslint": "^9.0.0",
+    "eslint-plugin-react": "^7.37.0",
     "jsdom": "^25.0.0",
     "sass": "^1.81.0",
     "typescript": "^5.6.0",
+    "typescript-eslint": "^8.0.0",
     "vite": "^6.0.0",
     "vitest": "^3.0.0"
   }

frontend/src/components/Layout/Header.tsx

@@ -5,7 +5,6 @@ import { Search, Bell, Plus, FileText, Loader2, Sun, Moon } from 'lucide-react';
 import { Button } from '@/components';
 import { useThemeStore } from '@/stores';
 import { api } from '@/services';
-// eslint-disable-next-line @typescript-eslint/no-unused-vars
 import type { Drawing } from '@/types';
 import styles from './Layout.module.scss';
 

frontend/src/components/Modal/Modal.tsx

@@ -32,7 +32,11 @@ export const Modal: React.FC<ModalProps> = ({
   useEffect(() => {
     const handleKey = (e: KeyboardEvent) => {
       if (e.key === 'Escape') {
-        onCancel?.() ?? onClose?.();
+        if (onCancel) {
+          onCancel();
+        } else {
+          onClose?.();
+        }
       }
     };
     if (isOpen) {

frontend/src/components/TemplatePicker/TemplatePicker.tsx

@@ -11,12 +11,14 @@ interface TemplatePickerProps {
   onSelect: (template: PickedTemplate) => void;
 }
 
+type RawElement = Record<string, unknown>;
+
 interface TemplateOption {
   id: PickedTemplate;
   label: string;
   description: string;
   icon: React.ElementType;
-  elements: any[];
+  elements: RawElement[];
 }
 
 function makeHandDrawnRect(x: number, y: number, w: number, h: number, text?: string) {
@@ -84,15 +86,16 @@ function makeText(x: number, y: number, text: string, fontSize = 20) {
 
 function makeCheckbox(x: number, y: number, checked = false) {
   const box = makeHandDrawnRect(x, y, 20, 20);
-  (box as any).backgroundColor = checked ? '#a5eba8' : 'transparent';
-  (box as any).customData = {
-    templateRole: 'checkbox',
-    checked,
-  };
-  return box;
+  return Object.assign(box, {
+    backgroundColor: checked ? '#a5eba8' : 'transparent',
+    customData: {
+      templateRole: 'checkbox',
+      checked,
+    },
+  });
 }
 
-export const BUILTIN_TEMPLATES: Record<PickedTemplate, any[]> = {
+export const BUILTIN_TEMPLATES: Record<PickedTemplate, RawElement[]> = {
   blank: [],
   todo: [
     makeHandDrawnRect(50, 50, 500, 50),

frontend/src/main.tsx

@@ -5,7 +5,9 @@ import './i18n';
 import { App } from './App';
 import './styles/global.scss';
 
-ReactDOM.createRoot(document.getElementById('root')!).render(
+const rootElement = document.getElementById('root');
+if (!rootElement) throw new Error('Root element not found');
+ReactDOM.createRoot(rootElement).render(
   <React.StrictMode>
     <BrowserRouter>
       <App />

frontend/src/pages/Editor/Editor.tsx

@@ -12,45 +12,40 @@ import styles from './Editor.module.scss';
 // Dynamic import for Excalidraw to avoid SSR issues
 const Excalidraw = React.lazy(() => import('@excalidraw/excalidraw').then(mod => ({ default: mod.Excalidraw })));
 
-interface ExcalidrawElement {
-  id: string;
-  type: string;
-  x: number;
-  y: number;
-  width: number;
-  height: number;
-  [key: string]: unknown;
-}
+import type { ExcalidrawElement } from '@excalidraw/excalidraw/types/element/types';
+import type { ExcalidrawImperativeAPI, ExcalidrawInitialDataState } from '@excalidraw/excalidraw/types/types';
 
-interface ExcalidrawState {
+type LooseElement = Record<string, unknown>;
+
+interface EditorState {
   elements: ExcalidrawElement[];
   appState: Record<string, unknown>;
   files: Record<string, { dataURL: string; mimeType: string }>;
 }
 
-function prepareElementsForImport(sourceElements: any[], offsetX: number, offsetY: number): any[] {
+function prepareElementsForImport(sourceElements: LooseElement[], offsetX: number, offsetY: number): LooseElement[] {
   if (!sourceElements || !sourceElements.length) return [];
   const idMap = new Map<string, string>();
-  sourceElements.forEach((el: any) => {
-    idMap.set(el.id, `${el.type}-${Math.random().toString(36).slice(2, 9)}`);
+  sourceElements.forEach((el) => {
+    idMap.set(el.id as string, `${el.type}-${Math.random().toString(36).slice(2, 9)}`);
   });
-  return sourceElements.map((el: any) => {
-    const newEl = { ...el };
-    newEl.id = idMap.get(el.id) || el.id;
-    newEl.x = (el.x || 0) + offsetX;
-    newEl.y = (el.y || 0) + offsetY;
-    newEl.version = (el.version || 1) + 1;
+  return sourceElements.map((el) => {
+    const newEl: LooseElement = { ...el };
+    newEl.id = idMap.get(el.id as string) || el.id;
+    newEl.x = ((el.x as number) || 0) + offsetX;
+    newEl.y = ((el.y as number) || 0) + offsetY;
+    newEl.version = ((el.version as number) || 1) + 1;
     newEl.versionNonce = Math.floor(Math.random() * 1000000);
     newEl.updated = Date.now();
     newEl.seed = Math.floor(Math.random() * 100000);
     if (newEl.boundElements) {
-      newEl.boundElements = newEl.boundElements.map((be: any) => ({
+      newEl.boundElements = (newEl.boundElements as LooseElement[]).map((be) => ({
         ...be,
-        id: idMap.get(be.id) || be.id,
+        id: idMap.get(be.id as string) || be.id,
       }));
     }
-    if (newEl.containerId && idMap.has(newEl.containerId)) {
-      newEl.containerId = idMap.get(newEl.containerId);
+    if (newEl.containerId && idMap.has(newEl.containerId as string)) {
+      newEl.containerId = idMap.get(newEl.containerId as string);
     }
     return newEl;
   });
@@ -71,7 +66,7 @@ export const Editor: React.FC = () => {
   const navigate = useNavigate();
   const [drawing, setDrawing] = useState<Drawing | null>(null);
   const [revisions, setRevisions] = useState<DrawingRevision[]>([]);
-  const [initialData, setInitialData] = useState<any>(null);
+  const [initialData, setInitialData] = useState<ExcalidrawInitialDataState | null>(null);
   const [isLoading, setIsLoading] = useState(true);
   const [isSaving, setIsSaving] = useState(false);
   const [saveStatus, setSaveStatus] = useState<'saved' | 'unsaved' | 'saving'>('saved');
@@ -81,11 +76,11 @@ export const Editor: React.FC = () => {
   const [notes, setNotes] = useState('');
   const [selectedRevision, setSelectedRevision] = useState<string | null>(null);
   const { theme: appTheme } = useThemeStore();
-  const currentStateRef = useRef<ExcalidrawState | null>(null);
+  const currentStateRef = useRef<EditorState | null>(null);
   const saveTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
   const lastSavedDataRef = useRef<string>('');
   const lastToggledCheckboxRef = useRef<string | null>(null);
-  const [excalidrawAPI, setExcalidrawAPI] = useState<any>(null);
+  const [excalidrawAPI, setExcalidrawAPI] = useState<ExcalidrawImperativeAPI | null>(null);
 
   const [showTemplates, setShowTemplates] = useState(false);
 
@@ -144,13 +139,13 @@ export const Editor: React.FC = () => {
   }, [id]);
 
   // Handle changes from Excalidraw
-  const handleExcalidrawChange = useCallback((elements: readonly unknown[], appState: Record<string, unknown>, files: Record<string, { dataURL: string; mimeType: string }>) => {
+  const handleExcalidrawChange = useCallback((elements: readonly ExcalidrawElement[], appState: Record<string, unknown>, files: Record<string, { dataURL: string; mimeType: string }>) => {
     const selectedIds = Object.keys((appState.selectedElementIds as Record<string, boolean> | undefined) || {});
     const selectedCheckbox = selectedIds.length === 1
-      ? (elements as any[]).find((el) => (
+      ? elements.find((el) => (
           el.id === selectedIds[0] &&
           !el.isDeleted &&
-          el.customData?.templateRole === 'checkbox'
+          (el.customData as Record<string, unknown> | undefined)?.templateRole === 'checkbox'
         ))
       : null;
 
@@ -158,23 +153,23 @@ export const Editor: React.FC = () => {
       lastToggledCheckboxRef.current = null;
     } else if (excalidrawAPI && lastToggledCheckboxRef.current !== selectedCheckbox.id) {
       lastToggledCheckboxRef.current = selectedCheckbox.id;
-      const nextChecked = !selectedCheckbox.customData?.checked;
-      const nextElements = (elements as any[]).map((el) => (
+      const nextChecked = !((selectedCheckbox.customData as Record<string, unknown> | undefined)?.checked as boolean);
+      const nextElements = elements.map((el) => (
         el.id === selectedCheckbox.id
           ? {
               ...el,
               backgroundColor: nextChecked ? '#a5eba8' : 'transparent',
               customData: {
-                ...(el.customData || {}),
+                ...((el.customData as Record<string, unknown> | undefined) || {}),
                 checked: nextChecked,
               },
-              version: (el.version || 1) + 1,
+              version: el.version + 1,
               versionNonce: Math.floor(Math.random() * 1000000),
               updated: Date.now(),
             }
           : el
       ));
-      excalidrawAPI.updateScene({ elements: nextElements });
+      excalidrawAPI.updateScene({ elements: nextElements as ExcalidrawElement[] });
       currentStateRef.current = {
         elements: nextElements,
         appState: appStateWithoutGrid(appState),
@@ -185,7 +180,7 @@ export const Editor: React.FC = () => {
     }
 
     currentStateRef.current = {
-      elements: elements as ExcalidrawElement[],
+      elements: elements as unknown as ExcalidrawElement[],
       appState: appStateWithoutGrid(appState),
       files,
     };
@@ -286,14 +281,14 @@ export const Editor: React.FC = () => {
     if (!templateElements || !excalidrawAPI) return;
     const currentElements = excalidrawAPI.getSceneElements?.() || [];
     let offsetX = 100;
-    let offsetY = 100;
+    const offsetY = 100;
     if (currentElements.length > 0) {
-      const maxX = Math.max(...currentElements.map((el: any) => (el.x || 0) + (el.width || 0)));
+      const maxX = Math.max(...currentElements.map((el) => (el.x + el.width)));
       offsetX = maxX + 100;
     }
     const newElements = prepareElementsForImport(templateElements, offsetX, offsetY);
     const mergedElements = [...currentElements, ...newElements];
-    excalidrawAPI.updateScene({ elements: mergedElements });
+    excalidrawAPI.updateScene({ elements: mergedElements as ExcalidrawElement[] });
     setShowTemplates(false);
     setSaveStatus('unsaved');
   };
@@ -407,7 +402,7 @@ export const Editor: React.FC = () => {
           {initialData && (
             <React.Suspense fallback={<div className={styles.loadingCanvas}>{t('editor.loadingCanvas')}</div>}>
               <Excalidraw
-                excalidrawAPI={(api: any) => setExcalidrawAPI(api)}
+                excalidrawAPI={(api: ExcalidrawImperativeAPI) => setExcalidrawAPI(api)}
                 initialData={initialData}
                 onChange={handleExcalidrawChange}
                 theme={appTheme === 'dark' ? 'dark' : 'light'}

frontend/src/pages/FileBrowser/FileBrowser.tsx

@@ -273,7 +273,12 @@ export const FileBrowser: React.FC = () => {
           <select
             className={styles.filterSelect}
             value={visibilityFilter}
-            onChange={(e) => setVisibilityFilter(e.target.value as any)}
+            onChange={(e) => {
+              const v = e.target.value;
+              if (v === 'all' || v === 'private' || v === 'team' || v === 'public-link') {
+                setVisibilityFilter(v);
+              }
+            }}
             aria-label="Filter by visibility"
             title="Filter by visibility"
           >
@@ -287,8 +292,12 @@ export const FileBrowser: React.FC = () => {
             value={`${sortBy}-${sortOrder}`}
             onChange={(e) => {
               const [sb, so] = e.target.value.split('-');
-              setSortBy(sb as any);
-              setSortOrder(so as any);
+              if (sb === 'name' || sb === 'updated' || sb === 'created') {
+                setSortBy(sb);
+              }
+              if (so === 'asc' || so === 'desc') {
+                setSortOrder(so);
+              }
             }}
             aria-label="Sort drawings"
             title="Sort drawings"

frontend/src/pages/Team/TeamSettings.tsx

@@ -70,8 +70,9 @@ export const TeamSettings: React.FC = () => {
       setNewEmail('');
       setNewPassword('');
       setNewRole('editor');
-    } catch (err: any) {
-      setError(err?.message || 'Failed to create user');
+    } catch (err: unknown) {
+      const message = err instanceof Error ? err.message : 'Failed to create user';
+      setError(message);
     } finally {
       setSending(false);
     }

frontend/src/pages/Templates/Templates.tsx

@@ -36,7 +36,7 @@ export const Templates: React.FC = () => {
     try {
       const t = await api.templates.create({ name: name.trim(), type: 'empty', scope: 'personal' });
       setTemplates([t, ...templates]); setShowModal(false); setName('');
-    } catch (err) { setError('Create failed'); }
+    } catch { setError('Create failed'); }
     finally { setCreating(false); }
   };