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• 句法
• 范例
• 规范
• 浏览器兼容性
• 相关话题

只读 length 特性为 DataTransferItemList interface returns the number of items currently in the drag item list.

句法

length = DataTransferItemList.length;
					

值

The number of drag data items in the list, or 0 if the list is empty or disabled. The drag item list is considered to be disabled if the item list's DataTransfer object is not associated with a drag data store.

范例

This example shows the use of the length 特性。

JavaScript

function dragstart_handler(ev) {
  console.log("dragStart");
  // Add this element's id to the drag payload so the drop handler will
  // know which element to add to its tree
  var dataList = ev.dataTransfer.items;
  dataList.add(ev.target.id, "text/plain");
  // Add some other items to the drag payload
  dataList.add("<p>... paragraph ...</p>", "text/html");
  dataList.add("http://www.example.org","text/uri-list");
}
function drop_handler(ev) {
  console.log("Drop");
  ev.preventDefault();
  var data = ev.dataTransfer.items;
  // Loop through the dropped items and log their data
  for (var i = 0; i < data.length; i++) {
    if ((data[i].kind == 'string') && (data[i].type.match('^text/plain'))) {
      // This item is the target node
      data[i].getAsString(function (s){
        ev.target.appendChild(document.getElementById(s));
      });
    } else if ((data[i].kind == 'string') && (data[i].type.match('^text/html'))) {
      // Drag data item is HTML
      data[i].getAsString(function (s){
        console.log("... Drop: HTML = " + s);
      });
    } else if ((data[i].kind == 'string') && (data[i].type.match('^text/uri-list'))) {
      // Drag data item is URI
      data[i].getAsString(function (s){
        console.log("... Drop: URI = " + s);
      });
    }
  }
}
function dragover_handler(ev) {
  console.log("dragOver");
  ev.preventDefault();
  // Set the dropEffect to move
  ev.dataTransfer.dropEffect = "move"
}
function dragend_handler(ev) {
  console.log("dragEnd");
  var dataList = ev.dataTransfer.items;
  // Clear any remaining drag data
  dataList.clear();
}
					

HTML

<div>
  <p id="source" ondragstart="dragstart_handler(event);" ondragend="dragend_handler(event);" draggable="true">
     Select this element, drag it to the Drop Zone and then release the selection to move the element.</p>
</div>
<div id="target" ondrop="drop_handler(event);" ondragover="dragover_handler(event);">Drop Zone</div>
					

CSS

div {
  margin: 0em;
  padding: 2em;
}
#source {
  color: blue;
  border: 1px solid black;
}
#target {
  border: 1px solid black;
}
					

结果

Drag and Drop demo link

规范

规范	状态	注释
HTML 实时标准 The definition of 'length' in that specification.	实时标准
HTML 5.1 The definition of 'length' in that specification.	推荐	Not included in W3C HTML5 推荐

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
length	Chrome 13	Edge 12	Firefox 50	IE No	Opera 12	Safari 6	WebView Android 4.4	Chrome Android 18	Firefox Android 50	Opera Android No	Safari iOS 6	Samsung Internet Android 1.0

图例

完整支持

完整支持

不支持

不支持

元数据

• 最后修改： 2019 年 3 月 23 日

相关话题

1. HTML 拖放 API
2. DataTransferItemList
3. 特性

   1. length
4. 方法

   1. add()
   2. clear()
   3. DataTransferItem()
   4. remove()
5. Related pages for HTML Drag and Drop API

   1. DataTransfer
   2. DataTransferItem
   3. DragEvent