Javascript: execute function by name

exec.js

executeFunctionByName = function(functionName)
{ 
  var args = Array.prototype.slice.call(arguments).slice(1);
  var namespaces = functionName.split(".");
  var func = namespaces.pop();
  var ns = namespaces.join('.');
  if(ns === undefined || ns === '')
  {
      ns = 'window';
  }

  ns = eval(ns);
  return ns[func].apply(ns, args);
};