Update to eslint v9

Switch to using `deno` as that allows referring to the config packages without
having to setup a `package.json` and other stuff required when running `eslint`
through `node` now.

.github/workflows/ci.yml

@@ -183,8 +183,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
+      - uses: denoland/setup-deno@v1
       - name: install `just`
         run: sudo snap install --edge --classic just
-      - run: npm install -g eslint@8
       - run: just lint-js

Justfile

@@ -15,4 +15,4 @@ lint:
   cargo clippy --all-features --all-targets --workspace --locked -- -D warnings
 
 lint-js:
-  eslint static templates gui-tests
+  deno run -A npm:eslint@9 static templates gui-tests eslint.config.js

eslint.config.js

@@ -0,0 +1,74 @@
+import js from "npm:@eslint/js@9";
+import globals from "npm:globals@15";
+
+export default [
+    js.configs.recommended,
+    {
+        languageOptions: {
+            ecmaVersion: 2022,
+        },
+        rules: {
+            "arrow-parens": ["error", "as-needed"],
+            "arrow-spacing": ["error", { before: true, after: true }],
+            "block-scoped-var": "error",
+            "brace-style": ["error", "1tbs", { allowSingleLine: false }],
+            "comma-dangle": ["error", "always-multiline"],
+            "comma-style": ["error", "last"],
+            "eol-last": ["error", "always"],
+            "eqeqeq": "error",
+            "func-call-spacing": ["error", "never"],
+            "guard-for-in": "error",
+            "key-spacing": ["error", { beforeColon: false, afterColon: true, mode: "strict" }],
+            "keyword-spacing": ["error", { before: true, after: true }],
+            "linebreak-style": ["error", "unix"],
+            "max-len": ["error", { code: 100, tabWidth: 4 }],
+            "no-alert": "error",
+            "no-confusing-arrow": "error",
+            "no-const-assign": "error",
+            "no-debugger": "error",
+            "no-div-regex": "error",
+            "no-dupe-args": "error",
+            "no-dupe-else-if": "error",
+            "no-dupe-keys": "error",
+            "no-duplicate-case": "error",
+            "no-ex-assign": "error",
+            "no-fallthrough": "error",
+            "no-floating-decimal": "error",
+            "no-implicit-globals": "error",
+            "no-implied-eval": "error",
+            "no-import-assign": "error",
+            "no-invalid-regexp": "error",
+            "no-label-var": "error",
+            "no-lonely-if": "error",
+            "no-mixed-operators": "error",
+            "no-multi-assign": "error",
+            "no-return-assign": "error",
+            "no-script-url": "error",
+            "no-self-compare": "error",
+            "no-sequences": "error",
+            "no-template-curly-in-string": "error",
+            "no-trailing-spaces": "error",
+            "no-unused-vars": ["error", { argsIgnorePattern: "^_", varsIgnorePattern: "^_" }],
+            "no-var": ["error"],
+            "prefer-arrow-callback": ["error"],
+            "prefer-const": ["error"],
+            "quotes": ["error", "double"],
+            "semi": ["error", "always"],
+            "space-before-blocks": "error",
+            "space-before-function-paren": ["error", "never"],
+            "space-infix-ops": "error",
+        },
+    },
+    {
+        files: ["static/**/*", "templates/**/*"],
+        languageOptions: {
+            globals: globals.browser,
+        },
+    },
+    {
+        files: ["gui-tests/**/*"],
+        languageOptions: {
+            globals: globals.node,
+        },
+    },
+];