DataTransfer.clearData()

DataTransfer.clearData() 方法删除给定类型的拖动操作的 drag data。如果给定类型的数据不存在,则此方法不执行任何操作。

如果调用此方法时没有传入参数,或者参数为空字符串,则将删除所有类型的数据。

此方法不会从拖动操作中删除文件,因此如果有任何文件包含在对象的 DataTransfer.types 列表中,仍然可能有一个类型为“Files”的条目在拖动。

备注: 该方法只能在 dragstart (en-US) 事件的处理程序中使用,因为这是拖动操作的数据存储唯一能写入的时间。

语法

DataTransfer.clearData([format]);

参数

format 可选

一个 string 指定要删除的数据类型。如果此参数为空字符串或未提供,则将删除所有类型的数据。

示例

这个例子显示了使用 DataTransfer 对象的 getData()setData() 以及 clearData() 方法。

HTML

<span class="tweaked" id="source" draggable="true">
  Select this element, drag it to the Drop Zone and then release the selection to move the element.
</span>
<span class="tweaked" id="target">Drop Zone</span>
<div>Status: <span id="status">Drag to start</span></div>
<div>Data is: <span id="data">uninitialized</span></div>

CSS

span.tweaked {
  display: inline-block;
  margin: 1em 0;
  padding: 1em 2em;
}
#source {
  color: blue;
  border: 1px solid black;
}
#target {
  border: 1px solid black;
}

JavaScript

window.addEventListener('DOMContentLoaded', function () {
  // Select HTML elements
  var draggable = document.getElementById('source');
  var dropable = document.getElementById('target');
  var status = document.getElementById('status');
  var data = document.getElementById('data');
  var dropped = false;
  // Register event handlers
  draggable.addEventListener('dragstart', dragStartHandler);
  draggable.addEventListener('dragend', dragEndHandler);
  dropable.addEventListener('dragover', dragOverHandler);
  dropable.addEventListener('dragleave', dragLeaveHandler);
  dropable.addEventListener('drop', dropHandler);
  function dragStartHandler (event) {
    status.textContent = 'Drag in process';
    // Change target element's border to signify drag has started
    event.currentTarget.style.border = '1px dashed blue';
    // Start by clearing existing clipboards; this will affect all types since we
    // don't give a specific type.
    event.dataTransfer.clearData();
    // Set the drag's format and data (use event target's id for data)
    event.dataTransfer.setData('text/plain', event.target.id);
    data.textContent = event.dataTransfer.getData('text/plain');
  }
  function dragEndHandler (event) {
    if (!dropped) {
      status.textContent = 'Drag canceled';
    }
    data.textContent = event.dataTransfer.getData('text/plain') || 'empty';
    // Change border to signify drag is no longer in process
    event.currentTarget.style.border = '1px solid black';
    if (dropped) {
      // Remove all event listeners
      draggable.removeEventListener('dragstart', dragStartHandler);
      draggable.removeEventListener('dragend', dragEndHandler);
      dropable.removeEventListener('dragover', dragOverHandler);
      dropable.removeEventListener('dragleave', dragLeaveHandler);
      dropable.removeEventListener('drop', dropHandler);
    }
  }
  function dragOverHandler (event) {
    status.textContent = 'Drop available';
    event.preventDefault();
  }
  function dragLeaveHandler (event) {
    status.textContent = 'Drag in process (drop was available)';
    event.preventDefault();
  }
  function dropHandler (event) {
    dropped = true;
    status.textContent = 'Drop done';
    event.preventDefault();
    // Get data linked to event format « text »
    var _data = event.dataTransfer.getData('text/plain');
    var element = document.getElementById(_data);
    // Append drag source element to event's target element
    event.target.appendChild(element);
    // Change CSS styles and displayed text
    element.style.cssText = 'border: 1px solid black;display: block; color: red';
    element.textContent = "I'm in the Drop Zone!";
  }
})

规范

Specification
HTML Standard
# dom-datatransfer-cleardata-dev

浏览器兼容性

BCD tables only load in the browser

参见