DataTransferItemList.length

DataTransferItemList 接口的只读属性length 返回当前拖动项列表中项目的数量.

语法

length = DataTransferItemList.length;

列表中拖动项的数量,如果列表为空或禁用则为0。如果列表的DataTransfer对象未与拖动数据存储关联,则认为拖动列表被禁用。

示例

这个例子演示了length 属性的用法。

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 备注
HTML Living Standard
length
Living Standard
HTML 5.1
length
Recommendation Not included in W3C HTML5 Recommendation

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
lengthChrome Full support 4Edge Full support 12Firefox Full support 50IE No support NoOpera Full support 12Safari No support NoWebView Android No support NoChrome Android No support NoFirefox Android Full support 50Opera Android No support NoSafari iOS No support NoSamsung Internet Android ?

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown