Extend Object Fully

extend.js

const uniqueElements = arr => [...new Set(arr)];

const getType = v =>
  v === undefined
    ? "undefined"
    : v === null
    ? "null"
    : v.constructor.name.toLowerCase();

const extendObject = (obj, obj2) => {
  for (let key in obj) {
    let item = obj[key];
    let typeIs = getType(item);
    let typeIs2 = getType(obj2[key]);
    if (typeIs !== "object") {
      if (typeIs === "array" && typeIs2 === "array") {
        obj[key] = uniqueElements([...obj[key], ...obj2[key]]);
      } else if (typeIs2 !== "array") {
        obj[key] = obj2[key];
      } else {
        obj[key] = { ...obj[key], ...obj2[key] };
      }
    } else if (typeIs2 === "object" && typeIs === "object") {
      extendObject(obj[key], obj2[key]);
    }
  }
  for (let key in obj2) {
    let item = obj2[key];
    let typeIs = getType(item);
    let typeIs2 = getType(obj[key]);
    if (typeIs !== "object") {
      if (typeIs === "array" && typeIs2 === "undefined") {
        obj[key] = item;
      } else if (typeIs2 === "undefined") {
        obj[key] = obj2[key];
      }
    } else if (typeIs2 === "object" && typeIs === "object") {
      extendObject(obj[key], obj2[key]);
    }
  }
};

module.exports = extendObject;