chore: Lint Typescript files using ESLint and add CI workflow linting

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

.eslintrc.json

@@ -0,0 +1,5 @@
+{
+	"extends": [
+		"@nextcloud/eslint-config/typescript"
+	]
+}

.github/workflows/lint-eslint.yml

@@ -0,0 +1,62 @@
+# This workflow is provided via the organization template repository
+#
+# https://github.com/nextcloud/.github
+# https://docs.github.com/en/actions/learn-github-actions/sharing-workflows-with-your-organization
+#
+# Use lint-eslint together with lint-eslint-when-unrelated to make eslint a required check for GitHub actions
+# https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/defining-the-mergeability-of-pull-requests/troubleshooting-required-status-checks#handling-skipped-but-required-checks
+
+name: Lint eslint
+
+on:
+  pull_request:
+    paths:
+      - '.github/workflows/**'
+      - 'lib/**'
+      - 'appinfo/info.xml'
+      - 'package.json'
+      - 'package-lock.json'
+      - 'tsconfig.json'
+      - '.eslintrc.*'
+      - '.eslintignore'
+      - '**.js'
+      - '**.ts'
+      - '**.vue'
+
+permissions:
+  contents: read
+
+concurrency:
+  group: lint-eslint-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    name: eslint
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+
+      - name: Read package.json node and npm engines version
+        uses: skjnldsv/read-package-engines-version-actions@8205673bab74a63eb9b8093402fd9e0e018663a1 # v2.2
+        id: versions
+        with:
+          fallbackNode: '^20'
+          fallbackNpm: '^9'
+
+      - name: Set up node ${{ steps.versions.outputs.nodeVersion }}
+        uses: actions/setup-node@e33196f7422957bea03ed53f6fbb155025ffc7b8 # v3
+        with:
+          node-version: ${{ steps.versions.outputs.nodeVersion }}
+
+      - name: Set up npm ${{ steps.versions.outputs.npmVersion }}
+        run: npm i -g npm@"${{ steps.versions.outputs.npmVersion }}"
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint

lib/index.ts

@@ -5,17 +5,17 @@
  * @throws if the key can't be found
  */
 export function loadState<T>(app: string, key: string, fallback?: T): T {
-    const elem = <HTMLInputElement>document.querySelector(`#initial-state-${app}-${key}`)
-    if (elem === null) {
-        if (fallback !== undefined) {
-            return fallback
-        }
-        throw new Error(`Could not find initial state ${key} of ${app}`)
-    }
+	const elem = <HTMLInputElement>document.querySelector(`#initial-state-${app}-${key}`)
+	if (elem === null) {
+		if (fallback !== undefined) {
+			return fallback
+		}
+		throw new Error(`Could not find initial state ${key} of ${app}`)
+	}
 
-    try {
-        return JSON.parse(atob(elem.value))
-    } catch (e) {
-       throw new Error(`Could not parse initial state ${key} of ${app}`)
-    }
+	try {
+		return JSON.parse(atob(elem.value))
+	} catch (e) {
+		throw new Error(`Could not parse initial state ${key} of ${app}`)
+	}
 }