chore: Migrated to ESlint (#790)

* chore: Migrated to ESlint

* Added licesne header

.eslintrc.js

@@ -0,0 +1,52 @@
+/*!
+ * Copyright 2020 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module.exports = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  plugins: [
+    '@typescript-eslint',
+  ],
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/eslint-recommended',
+    'plugin:@typescript-eslint/recommended',
+  ],
+  rules: {
+    // Following checks are temporarily disabled. We shall incrementally enable them in the
+    // future, fixing any violations as we go.
+    "@typescript-eslint/no-explicit-any": 0,
+    "@typescript-eslint/no-use-before-define": 0,
+    "@typescript-eslint/explicit-function-return-type": 0,
+    "@typescript-eslint/camelcase": 0,
+    "@typescript-eslint/no-inferrable-types": 0,
+    "@typescript-eslint/no-non-null-assertion": 0,
+    "@typescript-eslint/no-inferrable-types": 0,
+    "@typescript-eslint/no-var-requires": 0,
+    "@typescript-eslint/no-unused-vars": 0,
+    "@typescript-eslint/member-delimiter-style": 0,
+    "@typescript-eslint/no-empty-interface": 0,
+    "@typescript-eslint/no-array-constructor": 0,
+    "@typescript-eslint/ban-types": 0,
+    "no-case-declarations": 0,
+    "no-useless-escape": 0,
+    "no-prototype-builtins": 0,
+    "no-var": 0,
+
+    // Required checks
+    "indent": ["error", 2]
+  }
+};