Upgrade to eslint 10 and fix no-useless-assignment

.npmrc

@@ -0,0 +1,5 @@
+# eslint-plugin-import, eslint-plugin-react, eslint-plugin-jsx-a11y, and
+# eslint-plugin-jest-dom declare peer dependencies up to eslint@^9 but work
+# correctly with ESLint 10 via @eslint/compat fixupPluginRules().
+# Remove this once those plugins publish ESLint 10-compatible releases.
+legacy-peer-deps=true

eslint.config.js

@@ -1,5 +1,6 @@
 import js from '@eslint/js';
 import globals from 'globals';
+import { fixupPluginRules } from '@eslint/compat';
 import reactPlugin from 'eslint-plugin-react';
 import reactHooksPlugin from 'eslint-plugin-react-hooks';
 import jsxA11yPlugin from 'eslint-plugin-jsx-a11y';
@@ -46,10 +47,14 @@ export default [
     },
 
     plugins: {
-      import: importPlugin,
-      'jest-dom': jestDomPlugin,
-      'jsx-a11y': jsxA11yPlugin,
-      react: reactPlugin,
+      // eslint-plugin-import, react, jsx-a11y, and jest-dom still declare ESLint
+      // peer deps up to ^9; wrap them with fixupPluginRules so their internal use
+      // of removed context APIs (e.g. getFilename, getSourceCode) keeps working.
+      import: fixupPluginRules(importPlugin),
+      'jest-dom': fixupPluginRules(jestDomPlugin),
+      'jsx-a11y': fixupPluginRules(jsxA11yPlugin),
+      react: fixupPluginRules(reactPlugin),
+      // react-hooks and testing-library already declare ESLint 10 support
       'react-hooks': reactHooksPlugin,
       'testing-library': testingLibraryPlugin,
     },

package.json

@@ -83,8 +83,7 @@
     "@emotion/react": "^11.10.6",
     "@emotion/styled": "^11.10.6",
     "@eslint/compat": "^2.0.3",
-    "@eslint/eslintrc": "^3.3.5",
-    "@eslint/js": "^9.39.4",
+    "@eslint/js": "^10.0.0",
     "@mui/material": "^7.x",
     "@mui/system": "^7.x",
     "@testing-library/dom": "^10.4.0",
@@ -96,15 +95,15 @@
     "@vitest/ui": "^4.1.2",
     "bundlewatch": "^0.4.0",
     "chalk": "^5.3.0",
-    "eslint": "^9.39.4",
+    "eslint": "^10.0.0",
     "eslint-plugin-import": "^2.32.0",
     "eslint-plugin-jest-dom": "^5.5.0",
     "eslint-plugin-jsx-a11y": "^6.10.2",
     "eslint-plugin-react": "^7.37.5",
     "eslint-plugin-react-hooks": "^5.2.0",
     "eslint-plugin-testing-library": "^7.16.2",
     "glob": "^13.0.6",
-    "globals": "^15.15.0",
+    "globals": "^16.0.0",
     "happy-dom": "^20.0",
     "react": "^19.0.0",
     "react-dnd-test-backend": "^16.0.1",

src/components/AnnotationsOverlay.jsx

@@ -159,9 +159,8 @@ export function AnnotationsOverlay({
         };
       };
 
-      let annosWithScore = [];
       let radius = 1;
-      annosWithScore = sortBy(annos.map(annosWithClickScore(radius)), 'score');
+      let annosWithScore = sortBy(annos.map(annosWithClickScore(radius)), 'score');
 
       while (radius < Math.max(canvasWidth, canvasHeight)
         && annosWithScore[0].score === annosWithScore[1].score) {

src/components/ViewerNavigation.jsx

@@ -14,8 +14,8 @@ export function ViewerNavigation({
 }) {
   const { t } = useTranslation();
   let htmlDir = 'ltr';
-  let previousIconStyle = {};
-  let nextIconStyle = {};
+  let previousIconStyle;
+  let nextIconStyle;
   switch (viewingDirection) {
     case 'top-to-bottom':
       previousIconStyle = { transform: 'rotate(270deg)' };

src/components/WindowTopBarTitle.jsx

@@ -34,7 +34,7 @@ TitleTypography.propTypes = {
 export function WindowTopBarTitle({
   error = null, hideWindowTitle = false, isFetching = false, manifestTitle = '',
 }) {
-  let title = null;
+  let title;
   if (isFetching) {
     title = (
       <StyledTitleTypography>