function getKeyCode(e) {
    var code;
    if (!e) var e = window.event;
    if (e.keyCode) code = e.keyCode;
    else if (e.which) code = e.which;
    return code;
}

function handleBlur(e) {
    if (this.lastKey == 9)
        this.focus();
    return false;
}

function handleKeyDown(e) {
    code = getKeyCode(e);
    this.lastKey = code;
    if (code == 9) {
        return false;
    }
}

function handleFocus(e) {
    this.lastKey = null;
    code = getKeyCode(e);
    if (code == 9)
        return false;
}

window.onload = function() {
    document.onfocus = handleFocus;
    document.onblur = handleBlur;
    document.onkeydown = handleKeyDown;
};