extendsFunctionConstructor

// https://www.accelebrate.com/blog/javascript-es6-classes-and-prototype-inheritance-part-1-of-2/
// the extends function is not already defined within the current
// context; therefore, define it
export function extendClass({ childClass, parentClass }) {

    // mixin pattern for copying parent constructor function properties
    // as static properties to the child constructor function
    // properties on constructor function are commonly known as static
    // properties
    for (var parentPropertyName in parentClass) {
  
      // only copy properties specifically defined on the parent
      if (parentClass.hasOwnProperty(parentPropertyName)) {
        // for primitive types, this will copy the value,
        // for object types, this will copy the reference only
        childClass[parentPropertyName] = parentClass[parentPropertyName];
      }
  
    }
  
    // constructor function for the object that instantiated child objects
    // will inherit from
    // this function is unique within the context of each call to extend
  
    function __() {
        Object.defineProperty(this, 'constructor', { value: childClass }) //   this.constructor = childClass;
    }
  
    if (parentClass === null) {
  
      // objects instantiated with the child constructor function will
      // inherit from an object that inherits from nothing, not even
      // the built-in JavaScript Object
      childClass.prototype = Object.create(parentClass);
  
    } else {
  
      // assign the prototype property of the parent constructor function
      // to the prototype property of the constructor function defined
      // above
      __.prototype = parentClass.prototype;
  
      // create the object that all instances of the child will inherit
      // from, and assign it to the prototype property of the child
      // constructor function
      childClass.prototype = new __();
  
    }
  
  };