Upgrade ESLint from 8 to 9 with flat config migration

Replace .eslintrc.cjs with eslint.config.mjs, upgrade eslint-plugin-vue
to 10, eslint-plugin-cypress to 6, @vue/eslint-config-prettier to 10,
and remove @rushstack/eslint-patch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.eslintrc.cjs

@@ -1,20 +0,0 @@
-/* eslint-env node */
-require("@rushstack/eslint-patch/modern-module-resolution");
-
-module.exports = {
-  root: true,
-  extends: [
-    "plugin:vue/vue3-essential",
-    "eslint:recommended",
-    "@vue/eslint-config-prettier",
-  ],
-  overrides: [
-    {
-      files: ["cypress/e2e/**/*.{cy,spec}.{js,ts,jsx,tsx}"],
-      extends: ["plugin:cypress/recommended"],
-    },
-  ],
-  parserOptions: {
-    ecmaVersion: "latest",
-  },
-};

eslint.config.mjs

@@ -0,0 +1,17 @@
+import js from "@eslint/js";
+import pluginVue from "eslint-plugin-vue";
+import pluginCypress from "eslint-plugin-cypress";
+import skipFormatting from "@vue/eslint-config-prettier";
+
+export default [
+  {
+    files: ["**/*.{js,mjs,cjs,ts,vue}"],
+    ...js.configs.recommended,
+  },
+  ...pluginVue.configs["flat/essential"],
+  skipFormatting,
+  {
+    files: ["cypress/e2e/**/*.{cy,spec}.{js,ts,jsx,tsx}"],
+    ...pluginCypress.configs.recommended,
+  },
+];

package.json

@@ -48,20 +48,19 @@
   },
   "devDependencies": {
     "@4tw/cypress-drag-drop": "^2.3.1",
-    "@rushstack/eslint-patch": "^1.16.1",
     "@types/cytoscape": "^3.21.9",
     "@types/cytoscape-dagre": "^2.3.4",
     "@types/cytoscape-popper": "^2.0.4",
     "@types/node": "^20.19.37",
     "@vitejs/plugin-vue": "^5.2.4",
-    "@vue/eslint-config-prettier": "^7.0.0",
+    "@vue/eslint-config-prettier": "^10.2.0",
     "@vue/test-utils": "^2.4.6",
     "autoprefixer": "^10.4.27",
     "cypress": "^15.11.0",
     "cypress-xpath": "^2.0.1",
-    "eslint": "^8.22.0",
+    "eslint": "^9.39.3",
-    "eslint-plugin-cypress": "^2.15.2",
+    "eslint-plugin-cypress": "^6.1.0",
-    "eslint-plugin-vue": "^9.33.0",
+    "eslint-plugin-vue": "^10.8.0",
     "jsdom": "^28.1.0",
     "postcss": "^8.5.8",
     "prettier": "^3.8.1",
@@ -71,6 +70,7 @@
     "ts-node": "^10.9.2",
     "typescript": "^5.9.3",
     "vite": "^6.4.1",
-    "vitest": "^3.2.4"
+    "vitest": "^3.2.4",
+    "vue-eslint-parser": "^10.4.0"
   }
 }

src/main.ts

@@ -68,7 +68,7 @@ app.config.globalProperties.$cytoscape = cytoscape;
 
 // Cytoscape.js's style
 cytoscape.use( dagre );
-cytoscape.use( popper((ref: any) => ref) );
+cytoscape.use( popper((ref) => ref) );
 
 app.use(pinia);
 app.use(router);