gistfile1.js

var FN_ARGS = /^function\s*[^\(]*\(\s*([^\)]*)\)/m,
    FN_ARG_SPLIT = /,/,
    FN_ARG = /^\s*(_?)(\S+?)\1\s*$/,
    STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;

var fnSignature = function (fn) {
  var fnText = fn.toString().replace(STRIP_COMMENTS, ''),
      args   = fnText.match(FN_ARGS);
  if (!args) { return []; }
  return args[1].split(FN_ARG_SPLIT).map(function (arg) {
    return arg.trim();
  });
};

var addMagic = function (fn) {
  var sig = fnSignature(fn);
  sig.forEach(function (arg, i) {
    fn[arg] = function () {
      var args = [].slice.call(arguments).map(function (x) {
        return x.toString();
      }).join(", ");
      console.log(
        arg + " (parameter #" + i + ") called with [" + args + "]"
      );
      return fn;
    };
  });
};

var fn = function (a, b, c) { };

addMagic(fn);

fn.a(1, 2).b("test").c();