javascript 禁用F5等功能鍵

function window.onhelp()//屏蔽F1協助

{

    return false;

}

function document.onkeydown()

{

    if

            ((window.event.altKey && window.event.keyCode == 37) //屏蔽 Alt+ 方向鍵 ←

            || (window.event.altKey && window.event.keyCode == 39)//屏蔽 Alt+ 方向鍵 →

            || (window.event.ctrlKey && window.event.keyCode == 78)//CtrlN

            || (window.event.ctrlKey && window.event.keyCode == 82)//CtrlR

            || (window.event.keyCode == 116)//屏蔽 F5 

            )

    {

        window.event.keyCode = 0;

        window.event.returnvalue = false;

        return false;

    }

}