Parameterization of an object with the ability to set defaults.

param-with-defaults.js

function param(arrFields, callback) {
  for (var t, o = {}, defaults = [], len = arrFields.length, i = len; i--;) {
    t = o.toString.call(t = arrFields[i]) == '[object Array]' ? t : [t];
    defaults[i] = t[1];
    arrFields[i] = t[0];
  }

  return function(fields) {
    for (var t, args = arrFields.slice.call(arguments, 0), i = len; i--;) {
      args.unshift(fields && (o.hasOwnProperty.call(fields, t=arrFields[i]) ? fields[t] : defaults[i]));
    }
    return callback.apply(this, args);
  };
}

Let's define a function called random() which accepts min, max, and isInt. The min will default to 0 while max defaults to 1:

var random = param([['min', 0],['max', 1],'isInt'], function(min, max, isInt) {
  var ret = Math.random() * (max - min) + min;
  return isInt ? parseInt(ret) : ret;
});

It's as easy as that.