Support in all current engines.
This section defines an event-based drag-and-drop mechanism.
This specification does not define exactly what a drag-and-drop operation actually is.
On a visual medium with a pointing device, a drag operation could be the default action of a
mousedown event that is followed by a series of mousemove events, and the drop could be triggered by the mouse
being released.
When using an input modality other than a pointing device, users would probably have to explicitly indicate their intention to perform a drag-and-drop operation, stating what they wish to drag and where they wish to drop it, respectively.
However it is implemented, drag-and-drop operations must have a starting point (e.g. where the mouse was clicked, or the start of the selection or element that was selected for the drag), may have any number of intermediate steps (elements that the mouse moves over during a drag, or elements that the user picks as possible drop points as they cycle through possibilities), and must either have an end point (the element above which the mouse button was released, or the element that was finally selected), or be canceled. The end point must be the last element selected as a possible drop point before the drop occurs (so if the operation is not canceled, there must be at least one element in the middle step).
This section is non-normative.
To make an element draggable, give the element a draggable
attribute, and set an event listener for dragstart that
stores the data being dragged.
The event handler typically needs to check that it's not a text selection that is being
dragged, and then needs to store data into the DataTransfer object and set the
allowed effects (copy, move, link, or some combination).
For example:
<p>What fruits do you like?</p>
<ol ondragstart="dragStartHandler(event)">
<li draggable="true" data-value="fruit-apple">Apples</li>
<li draggable="true" data-value="fruit-orange">Oranges</li>
<li draggable="true" data-value="fruit-pear">Pears</li>
</ol>
<script>
var internalDNDType = 'text/x-example'; // set this to something specific to your site
function dragStartHandler(event) {
if (event.target instanceof HTMLLIElement) {
// use the element's data-value="" attribute as the value to be moving:
event.dataTransfer.setData(internalDNDType, event.target.dataset.value);
event.dataTransfer.effectAllowed = 'move'; // only allow moves
} else {
event.preventDefault(); // don't allow selection to be dragged
}
}
</script>To accept a drop, the drop target has to listen to the following events:
dragenter event handler reports
whether or not the drop target is potentially willing to accept the drop, by canceling the
event.dragover event handler specifies what feedback
will be shown to the user, by setting the dropEffect attribute of the
DataTransfer associated with the event. This event also needs to be canceled.drop event handler has a final chance to accept or
reject the drop. If the drop is accepted, the event handler must perform the drop operation on
the target. This event needs to be canceled, so that the dropEffect attribute's value can be used by the
source. Otherwise, the drop operation is rejected.For example:
<p>Drop your favorite fruits below:</p>
<ol ondragenter="dragEnterHandler(event)" ondragover="dragOverHandler(event)"
ondrop="dropHandler(event)">
</ol>
<script>
var internalDNDType = 'text/x-example'; // set this to something specific to your site
function dragEnterHandler(event) {
var items = event.dataTransfer.items;
for (var i = 0; i < items.length; ++i) {
var item = items[i];
if (item.kind == 'string' && item.type == internalDNDType) {
event.preventDefault();
return;
}
}
}
function dragOverHandler(event) {
event.dataTransfer.dropEffect = 'move';
event.preventDefault();
}
function dropHandler(event) {
var li = document.createElement('li');
var data = event.dataTransfer.getData(internalDNDType);
if (data == 'fruit-apple') {
li.textContent = 'Apples';
} else if (data == 'fruit-orange') {
li.textContent = 'Oranges';
} else if (data == 'fruit-pear') {
li.textContent = 'Pears';
} else {
li.textContent = 'Unknown Fruit';
}
event.target.appendChild(li);
}
</script>To remove the original element (the one that was dragged) from the display, the dragend event can be used.
For our example here, that means updating the original markup to handle that event:
<p>What fruits do you like?</p>
<ol ondragstart="dragStartHandler(event)" ondragend="dragEndHandler(event)">
...as before...
</ol>
<script>
function dragStartHandler(event) {
// ...as before...
}
function dragEndHandler(event) {
if (event.dataTransfer.dropEffect == 'move') {
// remove the dragged element
event.target.parentNode.removeChild(event.target);
}
}
</script>The data that underlies a drag-and-drop operation, known as the drag data store, consists of the following information:
A drag data store item list, which is a list of items representing the dragged data, each consisting of the following information:
The kind of data:
Text.
Binary data with a file name.
A Unicode string giving the type or format of the data, generally given by a MIME type. Some values that are not MIME types are special-cased for legacy reasons. The API does not enforce the use of MIME types; other values can be used as well. In all cases, however, the values are all converted to ASCII lowercase by the API.
There is a limit of one text item per item type string.
A Unicode or binary string, in some cases with a file name (itself a Unicode string), as per the drag data item kind.
The drag data store item list is ordered in the order that the items were added to the list; most recently added last.
The following information, used to generate the UI feedback during the drag:
A drag data store mode, which is one of the following:
For the dragstart event. New data can be added to the
drag data store.
For the drop event. The list of items representing dragged
data can be read, including the data. No new data can be added.
For all other events. The formats and kinds in the drag data store list of items representing dragged data can be enumerated, but the data itself is unavailable and no new data can be added.
A drag data store allowed effects state, which is a string.
When a drag data store is created, it
must be initialized such that its drag data store item list is empty, it has no
drag data store default feedback, it has no drag data store bitmap and
drag data store hot spot coordinate, its drag data store mode is protected mode, and its drag data store allowed effects
state is the string "uninitialized".
DataTransfer interfaceSupport in all current engines.
DataTransfer objects are used to expose the drag data store that
underlies a drag-and-drop operation.
[Exposed=Window]
interface DataTransfer {
constructor();
attribute DOMString dropEffect;
attribute DOMString effectAllowed;
[SameObject] readonly attribute DataTransferItemList items;
undefined setDragImage(Element image, long x, long y);
/* old interface */
readonly attribute FrozenArray<DOMString> types;
DOMString getData(DOMString format);
undefined setData(DOMString format, DOMString data);
undefined clearData(optional DOMString format);
[SameObject] readonly attribute FileList files;
};DataTransfer()Support in all current engines.
Creates a new DataTransfer object with an empty drag data
store.
dropEffect [ = value ]Support in all current engines.
Returns the kind of operation that is currently selected. If the kind of operation isn't one
of those that is allowed by the effectAllowed attribute, then the operation will
fail.
Can be set, to change the selected operation.
effectAllowed [ = value ]Support in all current engines.
Returns the kinds of operations that are to be allowed.
Can be set (during the dragstart event), to change
the allowed operations.
The possible values are "none",
"copy", "copyLink", "copyMove", "link", "linkMove", "move", "all", and "uninitialized",
itemsSupport in all current engines.
Returns a DataTransferItemList object, with the drag data.
setDragImage(element, x, y)Support in all current engines.
Uses the given element to update the drag feedback, replacing any previously specified feedback.
typesSupport in all current engines.
Returns a frozen array listing the formats that were set in the dragstart event. In addition, if any files are being
dragged, then one of the types will be the string "Files".
getData(format)Support in all current engines.
Returns the specified data. If there is no such data, returns the empty string.
setData(format, data)Support in all current engines.
Adds the specified data.
clearData( [ format ] )Support in all current engines.
Removes the data of the specified formats. Removes all data if the argument is omitted.
filesSupport in all current engines.
Returns a FileList of the files being dragged, if any.
DataTransfer objects that are created as part of drag-and-drop events are only valid while those events are being fired.
A DataTransfer object is associated with a drag data store while it
is valid.
A DataTransfer object has an associated types array, which is a
FrozenArray<DOMString>, initially empty. When the contents
of the DataTransfer object's drag data store item list change, or when
the DataTransfer object becomes no longer associated with a drag data
store, run the following steps:
Let L be an empty sequence.
If the DataTransfer object is still associated with a drag data
store, then:
For each item in the DataTransfer object's drag data store item
list whose kind
is text, add an entry to L consisting of the item's type string.
If there are any items in the DataTransfer object's drag data store
item list whose kind is File, then
add an entry to L consisting of the string "Files". (This
value can be distinguished from the other values because it is not lowercase.)
Set the DataTransfer object's types
array to the result of creating a frozen array from L.
The DataTransfer() constructor, when
invoked, must return a newly created DataTransfer object initialized as follows:
Set the drag data store's item list to be an empty list.
Set the drag data store's mode to read/write mode.
Set the dropEffect and
effectAllowed to "none".
The dropEffect attribute controls
the drag-and-drop feedback that the user is given during a drag-and-drop operation. When the
DataTransfer object is created, the dropEffect attribute is set to a string value. On
getting, it must return its current value. On setting, if the new value is one of "none", "copy", "link", or "move", then the attribute's current value must be
set to the new value. Other values must be ignored.
The effectAllowed attribute is
used in the drag-and-drop processing model to initialize the dropEffect attribute during the dragenter and dragover events. When the DataTransfer object is
created, the effectAllowed attribute is set
to a string value. On getting, it must return its current value. On setting, if drag data
store's mode is the read/write mode and the new value is one of "none", "copy", "copyLink", "copyMove", "link", "linkMove", "move", "all", or "uninitialized", then the attribute's
current value must be set to the new value. Otherwise it must be left unchanged.
The items attribute must return a
DataTransferItemList object associated with the DataTransfer object.
The setDragImage(element,
x, y) method must run the following steps:
If the DataTransfer object is no longer associated with a drag data
store, return. Nothing happens.
If the drag data store's mode is not the read/write mode, return. Nothing happens.
If element is an img element, then set the drag data store
bitmap to the element's image (at its intrinsic
size); otherwise, set the drag data store bitmap to an image generated from
the given element (the exact mechanism for doing so is not currently specified).
Set the drag data store hot spot coordinate to the given x, y coordinate.
The types attribute must return this
DataTransfer object's types
array.
The getData(format) method
must run the following steps:
If the DataTransfer object is no longer associated with a drag data
store, then return the empty string.
If the drag data store's mode is the protected mode, then return the empty string.
Let format be the first argument, converted to ASCII lowercase.
Let convert-to-URL be false.
If format equals "text", change it to "text/plain".
If format equals "url", change it to "text/uri-list" and set convert-to-URL to true.
If there is no item in the drag data store item list whose kind is text and whose type string is equal to format, return the empty string.
Let result be the data of the item in the drag data store item list whose kind is Plain Unicode string and whose type string is equal to format.
If convert-to-URL is true, then parse result as appropriate for
text/uri-list data, and then set result to the first URL from
the list, if any, or the empty string otherwise. [RFC2483]
Return result.
The setData(format,
data) method must run the following steps:
If the DataTransfer object is no longer associated with a drag data
store, return. Nothing happens.
If the drag data store's mode is not the read/write mode, return. Nothing happens.
Let format be the first argument, converted to ASCII lowercase.
If format equals "text", change it to "text/plain".
If format equals "url", change it to "text/uri-list".
Remove the item in the drag data store item list whose kind is text and whose type string is equal to format, if there is one.
Add an item to the drag data store item list whose kind is text, whose type string is equal to format, and whose data is the string given by the method's second argument.
The clearData() method must run the
following steps:
If the DataTransfer object is no longer associated with a drag data
store, return. Nothing happens.
If the drag data store's mode is not the read/write mode, return. Nothing happens.
If the method was called with no arguments, remove each item in the drag data store item list whose kind is Plain Unicode string, and return.
Let format be the first argument, converted to ASCII lowercase.
If format equals "text", change it to "text/plain".
If format equals "url", change it to "text/uri-list".
Remove the item in the drag data store item list whose kind is text and whose type string is equal to format, if there is one.
The clearData() method does not
affect whether any files were included in the drag, so the types attribute's list might still not be empty after
calling clearData() (it would still contain the
"Files" string if any files were included in the drag).
The files attribute must return a
live FileList sequence consisting of File objects
representing the files found by the following steps.
Furthermore, for a given FileList object and a given underlying file, the same
File object must be used each time.
Start with an empty list L.
If the DataTransfer object is no longer associated with a drag data
store, the FileList is empty. Return the empty list L.
If the drag data store's mode is the protected mode, Return the empty list L.
For each item in the drag data store item list whose kind is File , add the item's data (the file, in particular its name and contents, as well as its type) to the list L.
The files found by these steps are those in the list L.
This version of the API does not expose the types of the files during the drag.
DataTransferItemList interfaceSupport in all current engines.
Each DataTransfer object is associated with a DataTransferItemList
object.
[Exposed=Window]
interface DataTransferItemList {
readonly attribute unsigned long length;
getter DataTransferItem (unsigned long index);
DataTransferItem? add(DOMString data, DOMString type);
DataTransferItem? add(File data);
undefined remove(unsigned long index);
undefined clear();
};lengthSupport in all current engines.
Returns the number of items in the drag data store.
Returns the DataTransferItem object representing the indexth
entry in the drag data store.
remove(index)Support in all current engines.
Removes the indexth entry in the drag data store.
clear()Support in all current engines.
Removes all the entries in the drag data store.
add(data)Support in all current engines.
add(data, type)Adds a new entry for the given data to the drag data store. If the data is plain text then a type string has to be provided also.
While the DataTransferItemList object's DataTransfer object is
associated with a drag data store, the DataTransferItemList object's
mode is the same as the drag data store mode. When the
DataTransferItemList object's DataTransfer object is not
associated with a drag data store, the DataTransferItemList object's
mode is the disabled mode. The drag data store referenced in this
section (which is used only when the DataTransferItemList object is not in the
disabled mode) is the drag data store with which the
DataTransferItemList object's DataTransfer object is associated.
The length attribute must
return zero if the object is in the disabled mode; otherwise it must return the number of
items in the drag data store item list.
When a DataTransferItemList object is not in the disabled mode, its
supported property indices are the numbers in the range
0 .. n-1,
where n is the number of items in the drag data store item
list.
To determine the value of an indexed property
i of a DataTransferItemList object, the user agent must return a
DataTransferItem object representing the ith item in the
drag data store. The same object must be returned each time a particular item is
obtained from this DataTransferItemList object. The DataTransferItem
object must be associated with the same DataTransfer object as the
DataTransferItemList object when it is first created.
The add() method must run the
following steps:
If the DataTransferItemList object is not in the read/write mode, return null.
Jump to the appropriate set of steps from the following list:
If there is already an item in the drag data store item list whose kind is text and whose type string is equal to the value of the
method's second argument, converted to ASCII lowercase, then throw a
"NotSupportedError" DOMException.
Otherwise, add an item to the drag data store item list whose kind is text, whose type string is equal to the value of the method's second argument, converted to ASCII lowercase, and whose data is the string given by the method's first argument.
FileAdd an item to the drag data store item list whose kind is File, whose type
string is the type of the File,
converted to ASCII lowercase, and whose data is the same as the
File's data.
Determine the value of the indexed property
corresponding to the newly added item, and return that value (a newly created
DataTransferItem object).
The remove() method, when
invoked with the argument i, must run these steps:
If the DataTransferItemList object is not in the read/write mode, throw an
"InvalidStateError" DOMException.
Remove the ith item from the drag data store.
The clear() method, if the
DataTransferItemList object is in the read/write mode,
must remove all the items from the drag data store. Otherwise, it must do
nothing.
DataTransferItem interfaceSupport in all current engines.
Each DataTransferItem object is associated with a DataTransfer
object.
[Exposed=Window]
interface DataTransferItem {
readonly attribute DOMString kind;
readonly attribute DOMString type;
undefined getAsString(FunctionStringCallback? _callback);
File? getAsFile();
};
callback FunctionStringCallback = undefined (DOMString data);kindSupport in all current engines.
Returns the drag data item kind, one of: "string", "file".
typeSupport in all current engines.
Returns the drag data item type string.
getAsString(callback)Support in all current engines.
Invokes the callback with the string data as the argument, if the drag data item kind is text.
getAsFile()Support in all current engines.
Returns a File object, if the drag data item kind is File.
While the DataTransferItem object's DataTransfer object is associated
with a drag data store and that drag data store's drag data store
item list still contains the item that the DataTransferItem object represents,
the DataTransferItem object's mode is the same as the drag data store
mode. When the DataTransferItem object's DataTransfer object is
not associated with a drag data store, or if the item that the
DataTransferItem object represents has been removed from the relevant drag data
store item list, the DataTransferItem object's mode is the disabled
mode. The drag data store referenced in this section (which is used only when the
DataTransferItem object is not in the disabled mode) is the drag data
store with which the DataTransferItem object's DataTransfer
object is associated.
The kind attribute must return the
empty string if the DataTransferItem object is in the disabled mode; otherwise
it must return the string given in the cell from the second column of the following table from the
row whose cell in the first column contains the drag data item kind of the item
represented by the DataTransferItem object:
| Kind | String |
|---|---|
| Text | "string"
|
| File | "file"
|
The type attribute must return the
empty string if the DataTransferItem object is in the disabled mode; otherwise
it must return the drag data item type string of the item represented by the
DataTransferItem object.
The getAsString(callback) method must run the following steps:
If the callback is null, return.
If the DataTransferItem object is not in the read/write mode or the read-only mode,
return. The callback is never invoked.
If the drag data item kind is not text, then return. The callback is never invoked.
Otherwise, queue a task to invoke callback, passing the
actual data of the item represented by the DataTransferItem object as the
argument.
The getAsFile()
method must run the following steps:
If the DataTransferItem object is not in the read/write mode or the read-only mode,
then return null.
If the drag data item kind is not File, then return null.
Return a new File object representing the actual data of the item represented
by the DataTransferItem object.
DragEvent interfaceSupport in all current engines.
Support in all current engines.
The drag-and-drop processing model involves several events. They all use the
DragEvent interface.
[Exposed=Window]
interface DragEvent : MouseEvent {
constructor(DOMString type, optional DragEventInit eventInitDict = {});
readonly attribute DataTransfer? dataTransfer;
};
dictionary DragEventInit : MouseEventInit {
DataTransfer? dataTransfer = null;
};dataTransferSupport in all current engines.
Returns the DataTransfer object for the event.
Although, for consistency with other event interfaces, the DragEvent
interface has a constructor, it is not particularly useful. In particular, there's no way to
create a useful DataTransfer object from script, as DataTransfer objects
have a processing and security model that is coordinated by the browser during drag-and-drops.
The dataTransfer attribute of the
DragEvent interface must return the value it was initialized to. It represents the
context information for the event.
When a user agent is required to fire a DND event named e at an element, using a particular drag data store, and optionally with a specific related target, the user agent must run the following steps:
If no specific related target was provided, set related target to null.
Let window be the relevant global object of the
Document object of the specified target element.
If e is dragstart, then set the
drag data store mode to the read/write mode
and set dataDragStoreWasChanged to true.
If e is drop, set the drag data store
mode to the read-only mode.
Let dataTransfer be a newly created DataTransfer object
associated with the given drag data store.
Set the effectAllowed attribute to the drag data
store's drag data store allowed effects state.
Set the dropEffect attribute to "none" if e is dragstart, drag, or
dragleave; to the value corresponding to the
current drag operation if e is drop
or dragend; and to a value based on the effectAllowed attribute's value and the
drag-and-drop source, as given by the following table, otherwise (i.e. if e is dragenter or dragover):
effectAllowed | dropEffect |
|---|---|
"none" | "none" |
"copy" | "copy" |
"copyLink" | "copy", or, if appropriate, "link" |
"copyMove" | "copy", or, if appropriate, "move" |
"all" | "copy", or, if appropriate, either "link" or "move" |
"link" | "link" |
"linkMove" | "link", or, if appropriate, "move" |
"move" | "move" |
"uninitialized" when what is being dragged is a selection from a text control | "move", or, if appropriate, either "copy" or "link" |
"uninitialized" when what is being dragged is a selection | "copy", or, if appropriate, either "link" or "move" |
"uninitialized" when what is being dragged is an a element with an href attribute | "link", or, if appropriate, either "copy" or "move" |
| Any other case | "copy", or, if appropriate, either "link" or "move" |
Where the table above provides possibly appropriate alternatives, user agents may instead use the listed alternative values if platform conventions dictate that the user has requested those alternate effects.
For example, Windows platform conventions are such that dragging while
holding the "alt" key indicates a preference for linking the data, rather than moving or copying
it. Therefore, on a Windows system, if "link" is an option according to
the table above while the "alt" key is depressed, the user agent could select that instead of
"copy" or "move".
Let event be the result of creating an event using
DragEvent.
Initialize event's type attribute to
e, its bubbles attribute to true, its view attribute to window, its relatedTarget attribute to related
target, and its dataTransfer attribute to
dataTransfer.
If e is not dragleave or dragend, then initialize event's cancelable attribute to true.
Initialize event's mouse and key attributes initialized according to the state of the input devices as they would be for user interaction events.
If there is no relevant pointing device, then initialize event's screenX, screenY, clientX, clientY, and button attributes to 0.
Dispatch event at the specified target element.
Set the drag data store allowed effects state to the current value of
dataTransfer's effectAllowed
attribute. (It can only have changed value if e is dragstart.)
If dataDragStoreWasChanged is true, then set the drag data store mode back to the protected mode.
Break the association between dataTransfer and the drag data store.
When the user attempts to begin a drag operation, the user agent must run the following steps. User agents must act as if these steps were run even if the drag actually started in another document or application and the user agent was not aware that the drag was occurring until it intersected with a document under the user agent's purview.
Determine what is being dragged, as follows:
If the drag operation was invoked on a selection, then it is the selection that is being dragged.
Otherwise, if the drag operation was invoked on a Document, it is the first
element, going up the ancestor chain, starting at the node that the user tried to drag, that has
the IDL attribute draggable set to true. If there is no such
element, then nothing is being dragged; return, the drag-and-drop operation is never
started.
Otherwise, the drag operation was invoked outside the user agent's purview. What is being dragged is defined by the document or application where the drag was started.
img elements and a elements with an href attribute have their draggable attribute set to true by default.
Create a drag data store. All the DND events fired subsequently by the steps in this section must use this drag data store.
Establish which DOM node is the source node, as follows:
If it is a selection that is being dragged, then the source node is the
Text node that the user started the drag on (typically the Text node
that the user originally clicked). If the user did not specify a particular node, for example if
the user just told the user agent to begin a drag of "the selection", then the source
node is the first Text node containing a part of the selection.
Otherwise, if it is an element that is being dragged, then the source node is the element that is being dragged.
Otherwise, the source node is part of another document or application. When this specification requires that an event be dispatched at the source node in this case, the user agent must instead follow the platform-specific conventions relevant to that situation.
Multiple events are fired on the source node during the course of the drag-and-drop operation.
Determine the list of dragged nodes, as follows:
If it is a selection that is being dragged, then the list of dragged nodes contains, in tree order, every node that is partially or completely included in the selection (including all their ancestors).
Otherwise, the list of dragged nodes contains only the source node, if any.
If it is a selection that is being dragged, then add an item to the drag data store item list, with its properties set as follows:
text/plain"Otherwise, if any files are being dragged, then add one item per file to the drag data store item list, with their properties set as follows:
application/octet-stream" otherwise.Dragging files can currently only happen from outside a browsing context, for example from a file system manager application.
If the drag initiated outside of the application, the user agent must add items to the drag data store item list as appropriate for the data being dragged, honoring platform conventions where appropriate; however, if the platform conventions do not use MIME types to label dragged data, the user agent must make a best-effort attempt to map the types to MIME types, and, in any case, all the drag data item type strings must be converted to ASCII lowercase.
User agents may also add one or more items representing the selection or dragged element(s) in other forms, e.g. as HTML.
If the list of dragged nodes is not empty, then extract the microdata from those nodes into a JSON form, and add one item to the drag data store item list, with its properties set as follows:
application/microdata+jsonRun the following substeps:
Let urls be an empty list of absolute URLs.
For each node in the list of dragged nodes:
a element with an href attributehref content attribute relative to the
element's node document.img element with a src
attributesrc content attribute relative to the
element's node document.If urls is still empty, then return.
Let url string be the result of concatenating the strings in urls, in the order they were added, separated by a U+000D CARRIAGE RETURN U+000A LINE FEED character pair (CRLF).
Add one item to the drag data store item list, with its properties set as follows:
text/uri-listUpdate the drag data store default feedback as appropriate for the user agent (if the user is dragging the selection, then the selection would likely be the basis for this feedback; if the user is dragging an element, then that element's rendering would be used; if the drag began outside the user agent, then the platform conventions for determining the drag feedback should be used).
Fire a DND event named dragstart at the
source node.
If the event is canceled, then the drag-and-drop operation should not occur; return.
Since events with no event listeners registered are, almost by definition, never canceled, drag-and-drop is always available to the user if the author does not specifically prevent it.
Initiate the drag-and-drop operation in a manner consistent with platform conventions, and as described below.
The drag-and-drop feedback must be generated from the first of the following sources that is available:
From the moment that the user agent is to initiate the drag-and-drop operation, until the end of the drag-and-drop operation, device input events (e.g. mouse and keyboard events) must be suppressed.
During the drag operation, the element directly indicated by the user as the drop target is called the immediate user selection. (Only elements can be selected by the user; other nodes must not be made available as drop targets.) However, the immediate user selection is not necessarily the current target element, which is the element currently selected for the drop part of the drag-and-drop operation.
The immediate user selection changes as the user selects different elements (either by pointing at them with a pointing device, or by selecting them in some other way). The current target element changes when the immediate user selection changes, based on the results of event listeners in the document, as described below.
Both the current target element and the immediate user selection can be null, which means no target element is selected. They can also both be elements in other (DOM-based) documents, or other (non-web) programs altogether. (For example, a user could drag text to a word-processor.) The current target element is initially null.
In addition, there is also a current drag operation, which can take on the values
"none", "copy", "link", and "move". Initially, it has the value
"none". It is updated by the user agent
as described in the steps below.
User agents must, as soon as the drag operation is initiated and every 350ms (±200ms) thereafter for as long as the drag operation is ongoing, queue a task to perform the following steps in sequence:
If the user agent is still performing the previous iteration of the sequence (if any) when the next iteration becomes due, return for this iteration (effectively "skipping missed frames" of the drag-and-drop operation).
Fire a DND event named drag at the
source node. If this event is canceled, the user agent must set the current
drag operation to "none" (no
drag operation).
If the drag event was not canceled and the user has not
ended the drag-and-drop operation, check the state of the drag-and-drop operation, as
follows:
If the user is indicating a different immediate user selection than during the last iteration (or if this is the first iteration), and if this immediate user selection is not the same as the current target element, then update the current target element as follows:
Set the current target element to null also.
Set the current target element to the immediate user selection.
Fire a DND event named dragenter
at the immediate user selection.
If the event is canceled, then set the current target element to the immediate user selection.
Otherwise, run the appropriate step from the following list:
textarea, or an input element whose type attribute is in the Text state) or an editing host or
editable element, and the drag data store item list has an item
with the drag data item type string "text/plain" and the
drag data item kind textSet the current target element to the immediate user selection anyway.
Leave the current target element unchanged.
Fire a DND event named dragenter
at the body element, if there is one, or at the Document object,
if not. Then, set the current target element to the body
element, regardless of whether that event was canceled or not.
If the previous step caused the current target element to change, and if the
previous target element was not null or a part of a non-DOM document, then fire a DND
event named dragleave at the previous target
element, with the new current target element as the specific related
target.
If the current target element is a DOM element, then fire a DND
event named dragover at this current
target element.
If the dragover event is not canceled, run the
appropriate step from the following list:
textarea, or an input element whose type attribute is in the Text state) or an editing host or
editable element, and the drag data store item list has an item
with the drag data item type string "text/plain" and the drag
data item kind textSet the current drag operation to either "copy" or "move", as appropriate given the platform
conventions.
Reset the current drag operation to "none".
Otherwise (if the dragover event is
canceled), set the current drag operation based on the values of the effectAllowed and dropEffect attributes of the
DragEvent object's dataTransfer
object as they stood after the event dispatch
finished, as per the following table:
effectAllowed | dropEffect | Drag operation |
|---|---|---|
"uninitialized", "copy", "copyLink", "copyMove", or "all" | "copy" | "copy" |
"uninitialized", "link", "copyLink", "linkMove", or "all" | "link" | "link" |
"uninitialized", "move", "copyMove", "linkMove", or "all" | "move" | "move" |
| Any other case | "none" | |
Otherwise, if the current target element is not a DOM element, use platform-specific mechanisms to determine what drag operation is being performed (none, copy, link, or move), and set the current drag operation accordingly.
Update the drag feedback (e.g. the mouse cursor) to match the current drag operation, as follows:
| Drag operation | Feedback |
|---|---|
"copy" | Data will be copied if dropped here. |
"link" | Data will be linked if dropped here. |
"move" | Data will be moved if dropped here. |
"none" | No operation allowed, dropping here will cancel the drag-and-drop operation. |
Otherwise, if the user ended the drag-and-drop operation (e.g. by releasing the mouse button
in a mouse-driven drag-and-drop interface), or if the drag
event was canceled, then this will be the last iteration. Run the following steps, then stop the
drag-and-drop operation:
If the current drag operation is "none" (no drag operation), or, if the user
ended the drag-and-drop operation by canceling it (e.g. by hitting the Escape key),
or if the current target element is null, then the drag operation failed. Run
these substeps:
Let dropped be false.
If the current target element is a DOM element, fire a DND
event named dragleave at it; otherwise, if
it is not null, use platform-specific conventions for drag cancelation.
Set the current drag operation to "none".
Otherwise, the drag operation might be a success; run these substeps:
Let dropped be true.
If the current target element is a DOM element, fire a DND
event named drop at it; otherwise, use
platform-specific conventions for indicating a drop.
If the event is canceled, set the current drag operation to the value of the
dropEffect attribute of the
DragEvent object's dataTransfer
object as it stood after the event dispatch
finished.
Otherwise, the event is not canceled; perform the event's default action, which depends on the exact target as follows:
textarea, or an input element whose type attribute is in the Text state) or an editing host or
editable element, and the drag data store item list has an item
with the drag data item type string "text/plain" and the
drag data item kind textInsert the actual data of the first item in the drag data store item
list to have a drag data item type
string of "text/plain" and a drag
data item kind that is text into the text control or
editing host or editable element in a manner consistent with
platform-specific conventions (e.g. inserting it at the current mouse cursor position, or
inserting it at the end of the field).
Reset the current drag operation to "none".
Fire a DND event named dragend at the
source node.
Run the appropriate steps from the following list as the default action of the dragend event:
move", and the source of the
drag-and-drop operation is a selection in the DOM that is entirely contained within an
editing hostmove", and the source of the
drag-and-drop operation is a selection in a text controlThe user agent should delete the dragged selection from the relevant text control.
none"The drag was canceled. If the platform conventions dictate that this be represented to the user (e.g. by animating the dragged selection going back to the source of the drag-and-drop operation), then do so.
The event has no default action.
For the purposes of this step, a text control is a textarea element or
an input element whose type attribute is in
one of the
Text,
Search,
Tel,
URL,
Email,
Password, or
Number
states.
User agents are encouraged to consider how to react to drags near the edge of scrollable regions. For example, if a user drags a link to the bottom of the viewport on a long page, it might make sense to scroll the page so that the user can drop the link lower on the page.
This model is independent of which Document object the nodes involved
are from; the events are fired as described above and the rest of the processing model runs as
described above, irrespective of how many documents are involved in the operation.
This section is non-normative.
The following events are involved in the drag-and-drop model.
| Event name | Target | Cancelable? | Drag data store mode | dropEffect | Default Action |
|---|---|---|---|---|---|
dragstartSupport in all current engines. Firefox3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Source node | ✓ Cancelable | Read/write mode | "none" | Initiate the drag-and-drop operation |
dragFirefox🔰 3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Source node | ✓ Cancelable | Protected mode | "none" | Continue the drag-and-drop operation |
dragenterSupport in all current engines. Firefox3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Immediate user selection or the body element | ✓ Cancelable | Protected mode | Based on effectAllowed value | Reject immediate user selection as potential target element |
dragleaveSupport in all current engines. Firefox3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Previous target element | — | Protected mode | "none" | None |
dragoverSupport in all current engines. Firefox3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Current target element | ✓ Cancelable | Protected mode | Based on effectAllowed value | Reset the current drag operation to "none" |
dropSupport in all current engines. Firefox3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Current target element | ✓ Cancelable | Read-only mode | Current drag operation | Varies |
dragendFirefox🔰 3.5+Safari3.1+Chrome4+ Opera12+Edge79+ Edge (Legacy)12+Internet Explorer9+ Firefox AndroidNoSafari iOS11+Chrome AndroidNoWebView AndroidNoSamsung InternetNoOpera AndroidNo | Source node | — | Protected mode | Current drag operation | Varies |
Not shown in the above table: all these events bubble, are composed, and the effectAllowed attribute always has the value it had
after the dragstart event, defaulting to "uninitialized" in the dragstart event.
draggable attributeSupport in all current engines.
All HTML elements may have the draggable content attribute set. The draggable attribute is an enumerated attribute. It has
three states. The first state is true and it has the keyword true.
The second state is false and it has the keyword false. The third
state is auto; it has no keywords but it is the missing
value default and the invalid value default.
The true state means the element is draggable; the false state means that it is not. The auto state uses the default behavior of the user agent.
An element with a draggable attribute should also have a
title attribute that names the element for the purpose of
non-visual interactions.
draggable [ = value ]Returns true if the element is draggable; otherwise, returns false.
Can be set, to override the default and set the draggable
content attribute.
The draggable IDL
attribute, whose value depends on the content attribute's in the way described below, controls
whether or not the element is draggable. Generally, only text selections are draggable, but
elements whose draggable IDL attribute is true become
draggable as well.
If an element's draggable content attribute has the state
true, the draggable IDL attribute must return true.
Otherwise, if the element's draggable content attribute has
the state false, the draggable IDL attribute must return
false.
Otherwise, the element's draggable content attribute has
the state auto. If the element is an img element, an object
element that represents an image, or an a element with an href content attribute, the draggable IDL attribute must return true; otherwise, the draggable IDL attribute must return false.
If the draggable IDL attribute is set to the value false,
the draggable content attribute must be set to the literal
value "false". If the draggable IDL
attribute is set to the value true, the draggable content
attribute must be set to the literal value "true".
用户代理在 dragstart 事件对脚本可用的期间，
不得把数据添加到 DataTransfer 对象，
直到 drop 事件为止。
因为否则的话，如果用户从一个文档拖动敏感信息到第二个文档，过程中经过了一个恶意的第三个文档，
这个恶意的文档就可以截获数据。
同样的原因，只有在用户明确停止了拖动操作时用户代理才能认为拖放操作成功。
— 如果任何脚本停止了拖动操作，就必须把它视为未成功的（取消的）并且不得触发
drop 事件。
用户代理应该小心不要被脚本触发拖放操作。例如，在有鼠标和窗口的环境中， 如果在用户按下鼠标的过程中一个脚本移动了窗口，用户代理不得把它视为一个拖放操作。 这很重要，否则的话用户代理可能会在未经用户同意的情况下把数据从敏感数据源拖动到恶意的文档中。
在拖动和释放时，用户代理应该使用已知的安全特性白名单来过滤掉可能包含的活跃 （比如脚本）内容（比如 HTML）。类似地，应该把 相对 URL 转为绝对 URL 来避免引用发生预期之外的改变。本规范没有指定具体如何操作。
考虑一个恶意的页面，提供了一些内容并诱导用户选择和拖放（或者拷贝和粘贴）
该内容给一个受害页面 contenteditable 区域。
如果浏览器不确保拖动的只有安全内容，就可能释放（或粘贴）非安全内容（比如脚本和选中的事件处理器）
到受害站点，获取该站点的权限。可能因此导致跨站脚本攻击。