DataTransfer: clearData() 方法

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

如果此方法在没有参数的情况下被调用，或者格式为空字符串，则所有类型的拖动数据将被删除。

此方法不会删除拖动操作中的文件，因此如果拖动操作中包含任何文件，则对象中的 DataTransfer.types 列表中仍然可能存在类型为 "Files" 的条目。

注意：此方法只能在 dragstart 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可写的时间。

语法

js
clearData()
clearData(format)

参数

format 可选

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

返回值

无 (undefined)。

示例

此示例演示了如何使用 DataTransfer 对象的 getData()、setData() 和 clearData() 方法。

HTML

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

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

js
window.addEventListener("DOMContentLoaded", () => {
  // Select HTML elements
  const draggable = document.getElementById("source");
  const droppable = document.getElementById("target");
  const status = document.getElementById("status");
  const data = document.getElementById("data");
  let dropped = false;

  // Register event handlers
  draggable.addEventListener("dragstart", dragStartHandler);
  draggable.addEventListener("dragend", dragEndHandler);
  droppable.addEventListener("dragover", dragOverHandler);
  droppable.addEventListener("dragleave", dragLeaveHandler);
  droppable.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);
      droppable.removeEventListener("dragover", dragOverHandler);
      droppable.removeEventListener("dragleave", dragLeaveHandler);
      droppable.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 »
    const _data = event.dataTransfer.getData("text/plain");
    const 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

规范
HTML 标准
# dom-datatransfer-cleardata-dev

浏览器兼容性

BCD 表格仅在启用 JavaScript 的浏览器中加载。

另请参阅