feat: Add ESLint (#176)

.eslintrc.json

+{
+  "extends": "@excalidraw/eslint-config"
+}

.github/dependabot.yml

 version: 2
 updates:
-  - package-ecosystem: "npm"
-    directory: "/"
+  - package-ecosystem: npm
+    directory: /
     schedule:
-      interval: "weekly"
+      interval: weekly
+      day: sunday
+      time: "01:00"

.github/workflows/lint.yml

 jobs:
   lint:
     runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@v1
-
       - name: Setup Node.js 14.x
         uses: actions/setup-node@v1
         with:
           node-version: 14.x
-
       - name: Install dependencies
-        run: yarn
-
+        run: yarn --frozen-lockfile
       - name: Lint
-        run: yarn lint
+        run: yarn test:other

.github/workflows/publish-docker.yml

 jobs:
   publish-docker:
     runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@v2
       - uses: docker/build-push-action@v1

.github/workflows/test.yml

 jobs:
   test:
     runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@v1
-
       - name: Setup Node.js 14.x
         uses: actions/setup-node@v1
         with:
           node-version: 14.x
-
       - name: Install dependencies
-        run: yarn
-
+        run: yarn --frozen-lockfile
       - name: Test and Build
         run: |
-          yarn test
+          yarn test:code
           yarn build

package.json

 {
   "dependencies": {
+    "@excalidraw/eslint-config": "1.0.0",
     "@excalidraw/prettier-config": "1.0.2",
     "@types/debug": "4.1.5",
     "@types/express": "4.17.11",
     "@types/node": "14.14.31",
     "@types/socket.io": "2.1.4",
+    "@typescript-eslint/eslint-plugin": "4.16.1",
+    "@typescript-eslint/parser": "4.16.1",
     "debug": "4.3.1",
+    "eslint": "7.21.0",
+    "eslint-config-prettier": "8.1.0",
+    "eslint-plugin-prettier": "3.3.1",
     "express": "4.17.1",
     "prettier": "2.2.1",
     "socket.io": "2.3.0",
-    "ts-node-dev": "1.1.1",
-    "typescript": "4.1.5"
+    "ts-node-dev": "1.1.6",
+    "typescript": "4.2.2"
   },
   "license": "MIT",
   "main": "dist/index.js",
   "prettier": "@excalidraw/prettier-config",
   "scripts": {
     "build": "tsc",
-    "format": "yarn prettier --write",
-    "lint": "yarn prettier --list-different",
-    "prettier": "prettier \"**/*.{ts,md,json,yaml,yml}\"",
+    "fix:code": "yarn test:code --fix",
+    "fix:other": "yarn prettier --write",
+    "fix": "yarn fix:other && yarn fix:code",
+    "prettier": "prettier . --ignore-path=.gitignore",
     "start": "node dist/index.js",
     "start:dev": "ts-node-dev --respawn --transpile-only src/index.ts",
-    "test": "yarn lint"
+    "test:code": "eslint --ext .ts .",
+    "test:other": "yarn prettier --list-different",
+    "test": "yarn test:other && yarn test:code"
   },
   "version": "1.0.0"
 }

src/index.ts

 });
 
 const io = socketIO(server, {
-  handlePreflightRequest: function (req, res) {
+  handlePreflightRequest: (req, res) => {
     const headers = {
       "Access-Control-Allow-Headers": "Content-Type, Authorization",
       "Access-Control-Allow-Origin":