下面的例子可提示当鼠标按键被点击时 "ALT" 键是否已被按住 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>蜜蜂教程(mifengjc.com)</title>
  <script>
    function isKeyPressed(event) {
      if (event.altKey == 1) {
        alert(" ALT 键被按下!");
      } else {
        alert(" ALT 键没被按下!");
      }
    }
  </script>
</head>

<body onmousedown="isKeyPressed(event)">
  <p>点击该段落，尝试按下或者不按下shift 键的效果。</p>

</body>
</html>
        