禁止用户按F5刷新页面

document.onkeydown = function()
{
/*
(ctrlKey == true && keyCode == 82)   Ctrl+R   ---刷新
(keyCode == 116)                     F5       ---刷新
(ctrlKey == true && keyCode == 116)  Ctrl+F5  ---强制刷新
*/
    //window.alert(event.keyCode);
    var k = event.keyCode;
    if((event.ctrlKey == true && k == 82) || (k == 116) || (event.ctrlKey == true && k == 116))
    {
        //return (window.confirm("关闭?"));
        event.keyCode = 0;
        event.returnValue = false;
        event.cancelBubble = true;
    }
}