Add eslint.

javascript/.eslintrc.js

+module.exports = {
+  "extends": [
+    "eslint:recommended",
+    "plugin:import/errors",
+    "plugin:import/warnings"
+  ],
+  "parserOptions": {
+    "ecmaVersion": 8,
+    "sourceType": "module",
+    "ecmaFeatures": {
+      "jsx": true
+    }
+  },
+  "env": {
+    "es6": true,
+    "browser": true
+  },
+  "rules": {
+    "no-class-assign": 0,
+    "import/no-extraneous-dependencies": [
+      2,
+      {
+        "devDependencies": true
+      }
+    ],
+    "jsx-quotes": 2,
+    "eol-last": [
+      "error",
+      "always"
+    ],
+    "indent": [
+      "error",
+      2
+    ],
+    "no-multiple-empty-lines": [
+      "error",
+      {
+        "max": 1,
+        "maxBOF": 0,
+        "maxEOF": 1
+      }
+    ],
+    "keyword-spacing": [
+      "error",
+      {
+        "before": true,
+        "after": true
+      }
+    ],
+    "no-var": "error",
+    "space-before-function-paren": [
+      "error",
+      {
+        "anonymous": "always",
+        "named": "never",
+        "asyncArrow": "always"
+      }
+    ],
+    "eqeqeq": [
+      "error",
+      "always"
+    ],
+    "quotes": [
+      "error",
+      "single"
+    ],
+    "space-infix-ops": "error",
+    "brace-style": [
+      "error",
+      "1tbs",
+      {
+        "allowSingleLine": true
+      }
+    ],
+    "curly": "error",
+    "handle-callback-err": "error",
+    "operator-linebreak": [
+      "error",
+      "after"
+    ],
+    "block-spacing": "error",
+    "camelcase": "error",
+    "comma-dangle": [
+      "error",
+      "never"
+    ],
+    "comma-style": [
+      "error",
+      "last"
+    ],
+    "dot-location": [
+      "error",
+      "property"
+    ],
+    "func-call-spacing": [
+      "error",
+      "never"
+    ],
+    "key-spacing": [
+      "error",
+      {
+        "beforeColon": false,
+        "afterColon": true,
+        "mode": "strict"
+      }
+    ],
+    "new-cap": "error",
+    "new-parens": "error",
+    "no-eval": "error",
+    "no-extend-native": "error",
+    "no-extra-bind": "error",
+    "no-extra-parens": [
+      "error",
+      "all",
+      {
+        "conditionalAssign": false,
+        "returnAssign": false,
+        "nestedBinaryExpressions": false,
+        "ignoreJSX": "all",
+        "enforceForArrowConditionals": false
+      }
+    ],
+    "no-fallthrough": "error",
+    "no-floating-decimal": "error",
+    "no-implied-eval": "error",
+    "no-label-var": "error",
+    "no-lone-blocks": "error",
+    "no-mixed-spaces-and-tabs": "error",
+    "no-return-assign": "error",
+    "no-self-compare": "error",
+    "no-sequences": "error",
+    "no-shadow-restricted-names": "error",
+    "no-tabs": "error",
+    "no-template-curly-in-string": "error",
+    "no-throw-literal": "error",
+    "no-trailing-spaces": "error",
+    "no-undef-init": "error",
+    "no-unmodified-loop-condition": "error",
+    "no-unneeded-ternary": "error",
+    "no-useless-constructor": "error",
+    "no-whitespace-before-property": "error",
+    "no-with": "error",
+    "object-property-newline": "error",
+    "object-shorthand": "error",
+    "padded-blocks": [
+      "error",
+      "never"
+    ],
+    "rest-spread-spacing": [
+      "error"
+    ],
+    "semi-spacing": "error",
+    "space-before-blocks": "error",
+    "space-in-parens": [
+      "error",
+      "never"
+    ],
+    "space-unary-ops": "error",
+    "template-curly-spacing": "error",
+    "yoda": "error",
+    "prefer-const": [
+      "error",
+      {
+        "destructuring": "any",
+        "ignoreReadBeforeAssign": false
+      }
+    ],
+    "semi": "error"
+  }
+};

javascript/package.json

@@ -38,6 +38,9 @@
     "babel-polyfill": "^6.26.0",
     "clean-webpack-plugin": "^0.1.19",
     "core-js": "^2.5.7",
+    "eslint": "^5.3.0",
+    "eslint-plugin-import": "^2.14.0",
+    "eslint-plugin-jsx-a11y": "^6.1.1",
     "html-webpack-inline-source-plugin": "^0.0.10",
     "html-webpack-plugin": "^3.2.0",
     "webpack": "^4.23.1",