DataTransfer.dropEffect - Web APIs 编辑

The DataTransfer.dropEffect property controls the feedback (typically visual) the user is given during a drag and drop operation. It will affect which cursor is displayed while dragging. For example, when the user hovers over a target drop element, the browser's cursor may indicate which type of operation will occur.

When the DataTransfer object is created, dropEffect is set to a string value. On getting, it returns its current value. On setting, if the new value is one of the values listed below, then the property's current value will be set to the new value and other values will be ignored.

For the dragenter and dragover events, dropEffect will be initialized based on what action the user is requesting. How this is determined is platform specific, but typically the user can press modifier keys such as the alt key to adjust the desired action. Within event handlers for dragenter and dragover events, dropEffect should be modified if a different action is desired than the action that the user is requesting.

For the drop and dragend events, dropEffect will be set to the action that was desired, which will be the value dropEffect had after the last dragenter or dragover event. In a dragend event, for instance, if the desired dropEffect is "move", then the data being dragged should be removed from the source.

Syntax

dataTransfer.dropEffect;

Values

A DOMString representing the drag operation effect. The possible values are:

copy

A copy of the source item is made at the new location.

move

An item is moved to a new location.

link

A link is established to the source at the new location.

none

The item may not be dropped.

Assigning any other value to dropEffect has no effect and the old value is retained.

Example

This example shows the use of the dropEffect and effectAllowed properties.

HTML Content

<div>
  <p id="source" ondragstart="dragstart_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 Content

div {
  margin: 0em;
  padding: 2em;
}

#source {
  color: blue;
  border: 1px solid black;
}

#target {
  border: 1px solid black;
}

JavaScript Content

function dragstart_handler(ev) {
  console.log("dragStart: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);

  // Add this element's id to the drag payload so the drop handler will
  // know which element to add to its tree
  ev.dataTransfer.setData("text", ev.target.id);
  ev.dataTransfer.effectAllowed = "move";
}

function drop_handler(ev) {
  console.log("drop: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);
  ev.preventDefault();

  // Get the id of the target and add the moved element to the target's DOM
  var data = ev.dataTransfer.getData("text");
  ev.target.appendChild(document.getElementById(data));
}

function dragover_handler(ev) {
  console.log("dragOver: dropEffect = " + ev.dataTransfer.dropEffect + " ; effectAllowed = " + ev.dataTransfer.effectAllowed);
  ev.preventDefault();
  // Set the dropEffect to move
  ev.dataTransfer.dropEffect = "move"
}

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Drag and drop
• Drag Operations
• Recommended Drag Types
• Dragging and Dropping Multiple Items
• DataTransfer test - Paste or Drag