There are alot of bad practices being used in this code. It gives the impression that you've (ab)used JavaScript for a long time, but haven't actually bothered to read the 101 introduction to the language.

E.g.:

    try {
       eval('el.' + argv[1]);
       return el;
    } catch(e) {
       return null
    };

Why in the world would you do this? JavaScript has property access via bracket syntax for a reason:

    return el[argv[1]] || null;

Give this a read: https://developer.mozilla.org/en/a_re-introduction_to_javasc...