html运行实例（event_ondragover

代码示例：（标识：event_ondragover_dom）
<!DOCTYPE HTML>
<html>
<head>
<style>
#droptarget {
  float: left; 
  width: 200px; 
  height: 35px;
  margin: 55px;
  margin-top: 155px;
  padding: 10px;
  border: 1px solid #aaaaaa;
}
</style>
</head>
<body>

<p>本例使用 HTML DOM 将 "ondragstart" 和 "ondrag" 事件分配给 p 元素，并将 "ondragover" 和 "ondrop" 事件分配给 div 元素。</p>

<p draggable="true" id="dragtarget">把我拖进矩形！</p>

<div id="droptarget"></div>

<p style="clear:both;"><b>注释：</b>Internet Explorer 8 及更早版本或 Safari 5.1 及更早版本不支持 drag 事件。</p>

<p id="demo"></p>

<script>
var drag = document.getElementById("dragtarget");
var drop = document.getElementById("droptarget");

/* 在拖动目标上触发的事件 */
drag.ondragstart = function(event) {
  event.dataTransfer.setData("Text", event.target.id);
};

drag.ondrag = function(event) {
  document.getElementById("demo").innerHTML = "The p element is being dragged.";
};

/* 在放置目标上触发的事件 */
drop.ondragover = function(event) {
  event.preventDefault();
  document.getElementById("demo").innerHTML = "The p element is OVER the droptarget.";
  event.target.style.border = "4px dotted purple";
};

drop.ondrop = function(event) {
  event.preventDefault();
  var data = event.dataTransfer.getData("Text");
  event.target.appendChild(document.getElementById(data));
  document.getElementById("demo").innerHTML = "The p element was dropped.";
};
</script>

</body>
</html>