Extend (subclass) native Array

MyArray.js

function MyArray() {
  var array = [];
  if (arguments.length) {
    array.push.apply(array, arguments);
  }
  // note: use `Object.setPrototypeOf` instead of __proto__ to be truly standards-compliant
  array.__proto__ = MyArray.prototype;
  return array;
}

// inherit properties and methods
MyArray.prototype.__proto__ = Array.prototype;

// custom methods
MyArray.prototype.last = function() {
  var length = this.length;
  return (length === 0) ? undefined : this[length - 1];
};

// static methods (emulate those of native Array)
MyArray.isArray = function(value) {
  return (value instanceof MyArray);
};

MyArray.from = function() {
  var array = Array.from.apply(Array, arguments);
  array.__proto__ = MyArray.prototype;
  return array;
};

MyArray.of = function() {
  var array = Array.of.apply(Array, arguments);
  array.__proto__ = MyArray.prototype;
  return array;
};