Recommended Drag Types

The following describes the best practice to use when assigning data to be dragged.


拖拽文本的时候,使用 text/plain 类型。数据应该是被拖拽的字符串。例如:

event.dataTransfer.setData("text/plain", "This is text to drag")


建议你总是添加text/plain类型数据作为不支持其它类型的应用或投放目标的降级,除非没有可选的符合逻辑的文本。总是将纯文本类型添加在最后,因为这是最不具体的数据( as it is the least specific)。



var dt = event.dataTransfer;
dt.setData("text/uri-list", "");
dt.setData("text/plain", "");




#A second link


当得到一条拖放的链接,你需要确保你能处理包含多条链接以及注释的数据。出于便利考虑,特殊类型URL可以用来获得text/uri-list类型数据中的第一条合法的链接(译注:chrome则是得到text/uri-list的完整数据)。你不应该使用 URL 类型来添加数据,这样做只是设置了 text/uri-list 类型的数据。

var url = event.dataTransfer.getData("URL");

XUL Planet





var dt = event.dataTransfer;
dt.setData("text/html", "Hello there, <strong>stranger</strong>");
dt.setData("text/plain", "Hello there, stranger");

Dragging Files

A local file is dragged using the application/x-moz-file type with a data value that is an nsIFile object. Non-privileged web pages are not able to retrieve or modify data of this type. Because a file is not a string, you must use the mozSetDataAt method to assign the data. Similarly, when retrieving the data, you must use the mozGetDataAt method.

event.dataTransfer.mozSetDataAt("application/x-moz-file", file, 0);

If possible, you may also include the file URL of the file using both the text/uri-list and/or text/plain types. These types should be added last so that the more specific application/x-moz-file type has higher priority.

Multiple files will be received during a drop as mutliple items in the data transfer. See Dragging and Dropping Multiple Items for more details about this.

The following example shows how to create an area for receiving dropped files:

<listbox ondragenter="return checkDrag(event)"
         ondragover="return checkDrag(event)"

function checkDrag(event)
  return event.dataTransfer.types.contains("application/x-moz-file");

function doDrop(event)
  var file = event.dataTransfer.mozGetDataAt("application/x-moz-file", 0);
  if (file instanceof Components.interfaces.nsIFile)

In this example, the event returns false only if the data transfer contains the application/x-moz-file type. During the drop event, the data associated with the file type is retrieved, and the filename of the file is added to the listbox. Note that the instanceof operator is used here as the mozGetDataAt method will return an nsISupports that needs to be checked and converted into an nsIFile. This is also a good extra check in case someone made a mistake and added a non-file for this type.

Dragging Images

Direct image dragging is not commonly done. In fact, Mozilla does not support direct image dragging on Mac or Linux platforms. Instead, images are usually dragged only by their URLs. To do this, use the text/uri-list type as with other URL links. The data should be the URL of the image or a data URL if the image is not stored on a web site or disk. For more information about data URLs, see the data URL scheme.

As with other links, the data for the text/plain type should also contain the URL. However, a data URL is not usually as useful in a text context, so you may wish to exclude the text/plain data in this situation.

In chrome or other privileged code, you may also use the image/jpeg, image/png or image/gif types, depending on the type of image. The data should be an object which implements the nsIInputStream interface. When this stream is read, it should provide the data bits for the image, as if the image was a file of that type.

You should also include the application/x-moz-file type if the image is located on disk. In fact, this a common way in which image files are dragged.

It is important to set the data in the right order, from most specific to least specific. The image type such as image/jpeg should come first, followed by the application/x-moz-file type. Next, you should set the text/uri-list data and finally the text/plain data. For example:

var dt = event.dataTransfer;
dt.mozSetDataAt("image/png", stream, 0);
dt.mozSetDataAt("application/x-moz-file", file, 0);
dt.setData("text/uri-list", imageurl);
dt.setData("text/plain", imageurl);

Note that the mozGetDataAt method is used for non-text data. As some contexts may only include some of these types, it is important to check which type is made available when receiving dropped images.

Dragging Nodes

Nodes and elements in a document may be dragged using the application/x-moz-node type. This data for the type should be a DOM node. This allows the drop target to receive the actual node where the drag was started from. Note that callers from a different domain will not be able to access the node even when it has been dropped.

You should always include a plain text alternative for the node.

Dragging Custom Data

You can also use other types that you make up for custom purposes. You should strive to always include a plain text alternative unless that object being dragged is specific to a particular site or application. In this case, the custom type ensures that the data cannot be dropped elsewhere.

Dragging files to an operating system folder

There are cases in which you may want to add a file to an existing drag event session, and you may also want to write the file to disk when the drop operation happens over a folder in the operating system when your code receives notification of the target folder's location. This only works in extensions (or other privileged code) and the data flavor "application/moz-file-promise" should be used. The following sample offers an overview of this advanced case:

// currentEvent is a given existing drag operation event

currentEvent.dataTransfer.setData("text/x-moz-url", URL);
currentEvent.dataTransfer.setData("application/x-moz-file-promise-url", URL);
currentEvent.dataTransfer.setData("application/x-moz-file-promise-filename", leafName);
                  new dataProvider(success,error),
                  0, Components.interfaces.nsISupports);

function dataProvider(){} 

dataProvider.prototype = {
  QueryInterface : function(iid) {
    if (iid.equals(Components.interfaces.nsIFlavorDataProvider)
                  || iid.equals(Components.interfaces.nsISupports))
      return this;
    throw Components.results.NS_NOINTERFACE;
  getFlavorData : function(aTransferable, aFlavor, aData, aDataLen) {
    if (aFlavor == 'application/x-moz-file-promise') {
       var urlPrimitive = {};
       var dataSize = {};
       aTransferable.getTransferData('application/x-moz-file-promise-url', urlPrimitive, dataSize);
       var url = new String(urlPrimitive.value.QueryInterface(Components.interfaces.nsISupportsString));
       console.log("URL file orignal is = " + url);
       var namePrimitive = {};
       aTransferable.getTransferData('application/x-moz-file-promise-filename', namePrimitive, dataSize);
       var name = new String(namePrimitive.value.QueryInterface(Components.interfaces.nsISupportsString));
       console.log("target filename is = " + name);
       var dirPrimitive = {};
       aTransferable.getTransferData('application/x-moz-file-promise-dir', dirPrimitive, dataSize);
       var dir = dirPrimitive.value.QueryInterface(Components.interfaces.nsILocalFile);
       console.log("target folder is = " + dir.path);
       var file = Cc[';1'].createInstance(Components.interfaces.nsILocalFile);
       console.log("output final path is =" + file.path);
       // now you can write or copy the file yourself...


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