add eslint

.eslintrc.json

@@ -0,0 +1,96 @@
+{
+  "env": {
+    "browser": true,
+    "es6": true
+  },
+  "extends": "eslint:recommended",
+  "globals": {
+    "Atomics": "readonly",
+    "SharedArrayBuffer": "readonly"
+  },
+  "parserOptions": {
+    "ecmaVersion": 2018,
+    "sourceType": "module"
+  },
+  "rules": {
+    "eqeqeq": "error",
+    "no-await-in-loop": "error",
+    "no-console": "error",
+    "no-throw-literal": "error",
+    "no-unmodified-loop-condition": "error",
+    "no-unused-expressions": "error",
+    "no-useless-call": "error",
+    "no-useless-concat": "error",
+    "no-useless-return": "error",
+    "no-void": "error",
+    "no-warning-comments": "warn",
+    "prefer-promise-reject-errors": "error",
+    "prefer-regex-literals": "error",
+    "require-await": "error",
+    "require-unicode-regexp": "error",
+    "vars-on-top": "warn",
+    "wrap-iife": ["error", "any"],
+    "yoda": "error",
+    "no-dupe-else-if": "error",
+    "no-extra-parens": "error",
+    "no-import-assign": "error",
+    "no-setter-return": "error",
+    "require-atomic-updates": "error",
+    "accessor-pairs": "error",
+    "array-callback-return": "error",
+    "default-case": "warn",
+    "default-param-last": "error",
+    "dot-notation": "error",
+    "grouped-accessor-pairs": "warn",
+    "max-classes-per-file": "error",
+    "no-alert": "error",
+    "no-caller": "error",
+    "no-constructor-return": "error",
+    "no-else-return": "warn",
+    "no-empty-function": "error",
+    "no-eval": "error",
+    "no-extend-native": "error",
+    "no-extra-bind": "error",
+    "no-labels": "error",
+    "no-floating-decimal": "warn",
+    "no-implicit-coercion": "error",
+    "no-implied-eval": "error",
+    "no-invalid-this": "error",
+    "no-lone-blocks": "error",
+    "no-loop-func": "error",
+    "no-multi-str": "warn",
+    "no-new": "error",
+    "no-new-func": "error",
+    "no-new-wrappers": "error",
+    "no-octal-escape": "error",
+    "no-param-reassign": "warn",
+    "no-return-assign": "error",
+    "no-return-await": "error",
+    "no-script-url": "error",
+    "no-self-compare": "error",
+    "no-sequences": "error",
+    "no-undef-init": "error",
+    "no-use-before-define": "error",
+    "no-array-constructor": "error",
+    "no-bitwise": "warn",
+    "no-lonely-if": "warn",
+    "no-multi-assign": "warn",
+    "no-nested-ternary": "error",
+    "no-new-object": "error",
+    "prefer-exponentiation-operator": "warn",
+    "prefer-object-spread": "warn",
+    "quotes": ["warn", "single"],
+    "no-confusing-arrow": "error",
+    "no-duplicate-imports": "error",
+    "no-useless-computed-key": "error",
+    "no-useless-constructor": "error",
+    "no-useless-rename": "error",
+    "no-var": "error",
+    "prefer-arrow-callback": "warn",
+    "prefer-const": "warn",
+    "prefer-destructuring": "warn",
+    "prefer-numeric-literals": "error",
+    "prefer-rest-params": "error",
+    "prefer-spread": "error"
+  }
+}