Get input keypress and filter content before adding to input

javascript

init();

var pattern = /[A-Za-z0-9-\.]/i;
function inputDigitsOnly(e) {
    var chrTyped, chrCode = 0, evt = e ? e : event;
    if (evt.charCode != null)     chrCode = evt.charCode;
    else if (evt.which != null)   chrCode = evt.which;
    else if (evt.keyCode != null) chrCode = evt.keyCode;

    if (chrCode == 0) chrTyped = 'SPECIAL KEY';
    else chrTyped = String.fromCharCode(chrCode);

    //[test only:] display chrTyped on the status bar
    self.status = 'inputDigitsOnly: chrTyped = ' + chrTyped;

    //Digits, special keys & backspace [\b] work as usual:
    if (chrTyped.match(pattern)) return true;
    if (evt.altKey || evt.ctrlKey || chrCode < 28) return true;

    //Any other input? Prevent the default response:
    if (evt.preventDefault) evt.preventDefault();
    evt.returnValue = false;
    return false;
}

function addEventHandler(elem, eventType, handler) {
    if (elem.addEventListener) elem.addEventListener(eventType, handler, false);
    else if (elem.attachEvent) elem.attachEvent('on' + eventType, handler);
    else return false;
    return true;
}

function init() {
    addEventHandler(self.document.getElementById('site-name'), 'keypress', inputDigitsOnly);
}

source