禁用按键F5刷新，兼容chrome、firefox、IE

window.onload = function(){
var timer = null; //声明定时器变量
document.onkeydown = function(event){
clearTimeout(timer); //每次按键先清除定时器，避免定时器重复多开
var event = event || window.event;
var keycode = event.keyCode || event.which;
if(keycode == 116){
alert('触发F5按键');
if(event.preventDefault){ //chrome、firefox、IE9+
event.preventDefault();
}else{//IE8-
event.keyCode = 0;
event.returnValue = false;
}
timer = setTimeout(function(){ //设置一个定时器，3秒后清除按键事件，恢复按F5刷新功能
alert('恢复刷新');
document.onkeydown = null;
}, 3000);
}
};
};

window.onload = function(){
var timer = null;
if(document.addEventListener){//chrome、firefox、IE9+
document.addEventListener('keydown',shieldRefresh);
}else{//IE8-
document.attachEvent('onkeydown',shieldRefresh);
}

function shieldRefresh(event){
clearTimeout(timer);
var event = event || window.event;
var keycode = event.keyCode || event.which;
if(keycode == 116){
alert('触发F5按键');
if(event.preventDefault){//chrome、firefox、IE9+
event.preventDefault();
}else{//IE8-
event.keyCode = 0;
event.returnValue = false;
}
t
4000
imer = setTimeout(function(){
alert('恢复刷新');
if(document.removeEventListener){
document.removeEventListener('keydown',shieldRefresh);
}else{
document.detachEvent('onkeydown',shieldRefresh);
}
}, 3000);
}
}
};