Possible Duplicate:

Is there a (built-in) way in JavaScript to check if a string is a valid number?

i want to check whether a textbox contains a numeric value or a string using javascript
i used this.

var query=getquerystring()

    if(isNaN(query))



        {

           alert(query is a string);

        }

        else{

           alert(query is numeric);



        }

where getquerystring() is a function as

function getquerystring() {

            var query=document.getElementById(queryString).value;



            return  query;

         }

but when i enter a number 1234 in textbox still getting query is a string.
please tell me what is wrong in my code, and suggest me some solution.