A better way to create a function from a string is by using Function
:
var fn = Function("alert('hello there')");
fn();
This has as advantage / disadvantage that variables in the current scope (if not global) do not apply to the newly constructed function.
Passing arguments is possible too:
var addition = Function("a", "b", "return a + b;");
alert(addition(5, 3)); // shows '8'