F5 , Esc , BackSpace(BS) " keys

see the codes below:

My Java Script code will be ,
document.attachEvent("onkeydown", win_onkeydown_handler);

function win_onkeydown_handler() {
    switch (event.keyCode) {

    case 116 : // 'F5'
         event.returnValue = false;
         event.keyCode = 0;
         break;  

    case 27: // 'Esc'
        event.returnValue = false;
        event.keyCode = 0;
        break;

    case 08: // 'BackSpace'
        if (event.srcElement.tagName == "INPUT"
                || event.srcElement.tagName == "TEXTAREA") {
        } else {
            event.returnValue = false;
            event.keyCode = 0;
        }
        break;

    }
}