check for positive numbers using regular expression.

function CheckNumericValue(id) {
            var num = /^[0-9\s\+]+$/;
            var txt=document.getElementById(id).value;
            if (txt != "") {
                if (!txt.match(num)) {
                    alert("Please enter positive numbers only");
                    document.getElementById(id).focus()
                    return false;
                }
            }
            else {
                alert("Please enter some value in textbox.");
                document.getElementById(id).focus()
                return false;
            }
        }