ES6 extend method replicating $.extend Passes ESlint checking too! Added immutable arrays line 32

es6.extend.object.js

//
// Code taken from http://youmightnotneedjquery.com/
// THEN, edited to es6 and altered to work with ESlint
// 
// 1. extend objects the same as jQuery
// 2. passes eslint AirBnB
// 3. provides you with isTypeOf and isObject methods
// 4. Please remember to use Object.assign instead if object 1 deep
// You lucky people.
//
export default {
  isTypeOf(str, obj) {
    return `[object ${str}]` === Object.prototype.toString.call(obj);
  },

  isObject(obj) {
    return this.isTypeOf('Object', obj);
  },

  extend(..._args) {
    const out = {};
    const args = _args;

    for (let i = 0; i < args.length; i += 1) {
      const obj = args[i];

      if (obj && this.isObject(obj)) {
        Object.keys(obj).forEach((key) => {
          if (this.isObject(obj[key])) {
            out[key] = this.extend(out[key], obj[key]);
          } else if (this.isArray(obj[key])) {
            out[key] = [...obj[key]];
          } else {
            out[key] = obj[key];
          }
        });
      }
    }

    return out;
  }
}