tryhtml5_ev_onshow 在线代码实例

 <div contextmenu="mymenu">
<p>用鼠标右键单击黄色框区域查看上下文菜单</p>

<menu type="context" id="mymenu" onshow="myFunction()">
  <menuitem label="Refresh" onclick="window.location.reload();" icon="ico_reload.png">
  <menu label="分享...">
    <menuitem label="Twitter" icon="ico_twitter.png" onclick="window.open('//twitter.com/intent/tweet?text=' + window.location.href);">
    <menuitem label="Facebook" icon="ico_facebook.png" onclick="window.open('//facebook.com/sharer/sharer.php?u=' + window.location.href);">
  </menu>
  <menuitem label="发邮件到该页面" onclick="window.location='mailto:?body='+window.location.href;">
</menu>

</div>

<p><strong>注意：</strong>目前只有 Firefox 浏览器支持  onshow 属性。</p>

<script>
function myFunction() {
    alert("上下文菜单即将显示");
}
</script>