How to activate setInterval() incase a text control has the focus

Actually I have an update enquery into this point .

I have smth like that :

$(document).ready(function() {



setInterval(doSmth, 10000);

 function doSmth() {

        var result = document.getElementById("fooText").value;

        if (result != "") {            

                    doSmthElse(result);

                }

            });

        }

    }

});

I need to activate the interval ,that is fired each 10 seconds, in case only a text control has the focus else do nothing !!