[Admins]

There has never been an eval() function.
I don't think that adding such type of function would be really good, it would be much better to think of better ways of doing what you want to do. It would only be a hack.
Why not letting the joining npc provide a function which is called by your code? Since level makers are doing copy&paste anyway it shouldn't be a problem. I don't think providing a boolean evaluation inside the onCreated function is easier than to copy the check-function.