extend.js

/**
 * Usage
 *   function Base() {}
 *   Base.prototype. // anything
 *
 *   let Child = Base.extend({ prototype }, { static });
 *   let instance = new Child();
 */
function extend(props, statics) {
  let parent = this;
  function Child() {
    parent.apply(this, arguments);
  }
  Child.prototype = Object.assign(Object.create(parent.prototype), props);
  Child.prototype.constructor = Child;
  Object.assign(Child, statics);
  return Child;
}