javascript event preventDefault( )

Instructs the current event to bypass the normal operation it performs on the node. Once set, the mode cannot be undone for the current event. The following Netscape 6 event listener function for an onkeypress event allows only numbers to be entered into a text field:

function numsOnly(evt) {
    if (evt.charCode< 48 || evt.charCode > 57) {
        evt.preventDefault( );
    }
}