Adjust code to airbnb style guide, including eslint rules and prettier configuration for code base

plejd/.eslintrc.js

@@ -0,0 +1,39 @@
+// const path = require('path');
+
+// {
+//   "extends": ["airbnb-base", "plugin:prettier/recommended"],
+//   "plugins": ["prettier"],
+//   "rules": {
+//     "prettier/prettier": "error"
+//   }
+// }
+
+// eslint-disable-next-line no-undef
+module.exports = {
+  root: true,
+  extends: [
+    'airbnb-base',
+    // 'prettier',
+    // 'plugin:prettier/recommended'
+  ],
+  parser: 'babel-eslint',
+  // plugins: ['prettier'],
+  rules: getRules(),
+};
+
+function getRules() {
+  return {
+    // Allows modification of properties passed to functions.
+    // Notably used in array.forEach(e => {e.prop = val;})
+    'no-param-reassign': ['error', { props: false }],
+    // ++ operator widely used
+    'no-plusplus': ['off'],
+    // Hassio-Plejd team feals _ prefix is great for "private" variables.
+    // They will still be available for use from the outside
+    'no-underscore-dangle': ['off'],
+    // Allow function hoisting to improve code readability
+    'no-use-before-define': ['error', { functions: false, classes: true, variables: true }],
+    // Allow direct indexing of arrays only (array[0])
+    'prefer-destructuring': ['error', { array: false, object: true }],
+  };
+}