gistfile1.js

function Base() {
  var privateVariable;
  this._protectedVariable;
  this.publicVariable;
  function privateFunction() {}
}

Base.prototype._protectedFunction = function () {};

Base.prototype.publicFunction = function () {};

function Derived() {
  Base.call(this)
}

Derived.prototype = Object.create(Base.prototype);
Derived.prototype.constructor = Derived;

Derived.prototype._protectedFunction = function () {
  Base.prototype._protectedFunction.call(this)
};

Derived.prototype.publicFunction = function () {
  Base.prototype.publicFunction.call(this)
};