extends_other.js

function Other(args) {
  Original.call(this, args);
};
inherits(Other, Original);

// Yes, I know they are not actually "classes"
Other.prototype.classMethod = function() {
  // called like so: 
  // var other = New Other()
  // other.classMethod()
}

inherits.js

function inherits(clazz, sup) {
  clazz.prototype = Object.create(sup.prototype);
  clazz.prototype.constructor = clazz;
}