dom三个事件

1,页面加载后 window.onload=function(){};

2,页面(关闭)卸载后触发 window.onunload=function(){};

3,页面关闭前触发 window.onbeforeunload=function(){};

例子:页面刷新

<input type="button" name="name" value="刷新" id="btn" />
<script type="text/javascript">
window.onload = function () {
            document.getElementById('btn').onclick = function () {
                window.location.reload();
            };
        };
</script>