Add ESLint configuration and fix code formatting

Author: jaschadub

javascript/.eslintrc.cjs

@@ -0,0 +1,24 @@
+module.exports = {
+    env: {
+        browser: true,
+        es2021: true,
+        node: true
+    },
+    extends: [
+        'eslint:recommended'
+    ],
+    parserOptions: {
+        ecmaVersion: 'latest',
+        sourceType: 'module'
+    },
+    rules: {
+        'indent': ['error', 4],
+        'linebreak-style': ['error', 'unix'],
+        'quotes': ['error', 'single'],
+        'semi': ['error', 'always'],
+        'no-unused-vars': ['warn', { 'argsIgnorePattern': '^_' }],
+        'no-console': 'off',
+        'no-constant-condition': 'warn',
+        'no-empty': 'warn'
+    }
+};