Javascript / My dynamic function is it safe?

Possible Duplicate:
How to run user-submitted scripts securely in a node.js sandbox?

I want that my user can create their own format function that work with a particular object. I find two ways of doing it but I don't know if that functions can be hacked. It is run inside nodeJS.

//First way with eval (evil ?)
function convertObj(formula) {
   return function (obj) {
        return eval(formula);
    };
}

// Second way with function (same as eval ?)
function convertObj2(formula) {
  return new Function("obj", "return " + formula);
}

var inst = {
      "name": "BOB",
      "age": "30"    
    };

var formula = "obj.name.toLowerCase() + ' is ' + obj.age + ' years old'";

var next = convertObj(formula);
var next2 = convertObj2(formula);

document.write('<p>' + next(inst) + '</p>');
document.write('<p>' + next2(inst) + '</p>');​

Print

bob is 30 years old
bob is 30 years old

The example is also available at http://jsfiddle.net/DeWYy/2/