For Medium Article: https://medium.com/swlh/protect-your-javascript-applications-from-api-data-401a73c7c80b

exampleBaseModel1.js

import LocationModel from './LocationModel';
import CarModel from './CarModel';

class PersonModel {
  firstName = '';
  lastName = '';
  age = 0;
  address = null
  cars = [];

  /*
   * firstName & lastName will be an empty string if there is no data.
   * age will be zero if there is no data
   * address will be a new LocationModel or null if there is no data
   * cars will be an array of CarModel's or an empty array if there is no data
   */
  constructor(data) {
    this.firstName = data.firstName || '';
    this.lastName = data.lastName || '';
    this.age = isNaN(data.age) ? 0 : data.age;
    this.address = data.address ? new LocationModel(data.address) : null;
    this.cars = this._safelyCreateArrayData(data.cars, CarModel);
  }

  _safelyCreateArrayData(dataForArray, Model) {
    // if dataForArray is undefined or null, return empty array
    if (dataForArray == null) {
      return [];
    }

    // if dataForArray is a valid array, create array of models
    if (Array.isArray(dataForArray)) {
      return dataForArray.map((model) => new Model(model))
    }

    // if dataForArray is a single object, create a model and return an array
    return [
      new Model(dataForArray)
    ];
  }
}