[devote]

function validate(evt) {
    var theEvent = evt || window.event;
    var target = theEvent.target || theEvent.srcElement;
    var key = theEvent.keyCode || theEvent.which;
    key = String.fromCharCode(key);
    var regex = /[0-9]|/;
    if( !regex.test(key) || (!target.value.length && !+key)) {
        theEvent.returnValue = false;
        if(theEvent.preventDefault) theEvent.preventDefault();
    }
}