这是来自MDN的拖动示例，我无法获得ondragstart部分。
ondragstart =＆＃34; event.dataTransfer.setData（＆＃39; text / plain的＆＃39;，NULL）＆＃34;＆GT;
我可以知道为什么会这样吗？因为没有它，代码似乎工作正常。何时需要getData()？
<div class="dropzone"> <div id="draggable" draggable="true" ondragstart="event.dataTransfer.setData('text/plain',null)">
This div is draggable </div> </div> <div class="dropzone"></div> <div class="dropzone"></div> <div class="dropzone"></div>
<style> #draggable {
width: 200px;
height: 20px;
text-align: center;
background: white; }
.dropzone {
width: 200px;
height: 20px;
background: blueviolet;
margin-bottom: 10px;
padding: 10px; } </style>
<script>
var dragged;
/* events fired on the draggable target */ document.addEventListener("drag", function( event ) {
}, false);
document.addEventListener("dragstart", function( event ) {
// store a ref. on the dragged elem
dragged = event.target;
// make it half transparent
event.target.style.opacity = .5; }, false);
document.addEventListener("dragend", function( event ) {
// reset the transparency
event.target.style.opacity = ""; }, false);
/* events fired on the drop targets */ document.addEventListener("dragover", function( event ) {
// prevent default to allow drop
event.preventDefault(); }, false);
document.addEventListener("dragenter", function( event ) {
// highlight potential drop target when the draggable element enters it
if ( event.target.className == "dropzone" ) {
event.target.style.background = "purple";
}
}, false);
document.addEventListener("dragleave", function( event ) {
// reset background of potential drop target when the draggable element leaves it
if ( event.target.className == "dropzone" ) {
event.target.style.background = "";
}
}, false);
document.addEventListener("drop", function( event ) {
// prevent default action (open as link for some elements)
event.preventDefault();
// move dragged elem to the selected drop target
if ( event.target.className == "dropzone" ) {
event.target.style.background = "";
dragged.parentNode.removeChild( dragged );
event.target.appendChild( dragged );
}
}, false);
</script>