example.js

var new = function _new(Constructor) {
  var thisObj = Object.create(Constructor.prototype);
  var args = Array.prototype.slice.call(arguments, 1);
  var retObj = Constructor.apply(thisObj, args);
  if (typeof retObj === "object") {
    return retObj;
  } else {
    return thisObj
  }
};

var F = function() { };
F.prototype.a = 42;
var o = new(F);