function isNumberKey(evt) {
    var myValidChars = new Array(0, 8, 46, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57);
    var charCode = (evt.which) ? evt.which : event.keyCode
    if (charCode in oc(myValidChars))
        return true;
    return false;
}

function oc(a) {
    var o = {};
    for (var i = 0; i < a.length; i++) {
        o[a[i]] = '';
    }
    return o;
}