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This specification is the 13 September 2011 Last Call Working Draft. The Last Call review period will end on 11 October 2011.
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This section is non-normative.
User Agents that run on terminals which provide touch input to use web applications typically use interpreted mouse events to allow users to access interactive web applications. However, these interpreted events, being normalized data based on the physical touch input, tend to have limitations on delivering the intended user experience. Additionally, it is not possible to handle concurrent input regardless of device capability, due to constraints of mouse events: both system level limitations and legacy compatibility.
Meanwhile, native applications are capable of handling both cases with the provided system APIs.
The Touch Events specification provides a solution to this problem by specifying interfaces to allow web applications to directly handle touch events, and multiple touch points for capable devices.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words must, must not, required, should, should not, recommended, may, and optional in this specification are to be interpreted as described in [RFC2119].
This specification defines conformance criteria that apply to a single product: the user agent that implements the interfaces that it contains.
Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification [WEBIDL] as this specification uses that specification and terminology.
A conforming implementation is required to implement all fields defined in this specification.
Touch
Interface
This interface defines an individual point of contact for a touch
event. Touch
objects are immutable; after one is created, its
attributes must not change.
interface Touch {
readonly attribute long identifier;
readonly attribute long screenX;
readonly attribute long screenY;
readonly attribute long clientX;
readonly attribute long clientY;
readonly attribute long pageX;
readonly attribute long pageY;
};
clientX
of type long, readonlyclientY
of type long, readonlyidentifier
of type long, readonlypageX
of type long, readonlypageY
of type long, readonlyscreenX
of type long, readonlyscreenY
of type long, readonlyTouchList
Interface
This interface defines a list of individual points of contact for a
touch event. TouchList
objects are immutable; after one is
created, its contents must not change.
interface TouchList {
readonly attribute unsigned long length;
getter Touch item (unsigned long index);
Touch
identifiedTouch (long identifier);
};
length
of type unsigned long, readonlyTouch
es in the list
identifiedTouch
Touch
item in the list whose identifier property matches the specified identifier
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
identifier | long | ✘ | ✘ |
Touch
item
Touch
at the specified index in the list
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
index | unsigned long | ✘ | ✘ |
getter Touch
TouchEvent
Interface
This interface defines the touchstart, touchend,
touchmove, and touchcancel event types.
TouchEvent
objects are immutable; after one is created and
initialized, its attributes must not change.
interface TouchEvent : UIEvent {
readonly attribute TouchList
touches;
readonly attribute TouchList
targetTouches;
readonly attribute TouchList
changedTouches;
readonly attribute boolean altKey;
readonly attribute boolean metaKey;
readonly attribute boolean ctrlKey;
readonly attribute boolean shiftKey;
void initTouchEvent (DOMString type, boolean canBubble, boolean cancelable, AbstractView view, long detail, boolean ctrlKey, boolean altKey, boolean shiftKey, boolean metaKey, TouchList
touches, TouchList
targetTouches, TouchList
changedTouches);
};
altKey
of type boolean, readonlytrue
if the alt (Alternate) key modifier is activated;
otherwise false
changedTouches
of type TouchList
, readonly
a list of Touch
es for every point of contact which contributed
to the event.
For the touchstart event this must be a list of the touch points that just became active with the current event. For the touchmove event this must be a list of the touch points that have moved since the last event. For the touchend event this must be a list of the touch points that have just been removed from the surface.
ctrlKey
of type boolean, readonlytrue
if the ctrl (Control) key modifier is activated;
otherwise false
metaKey
of type boolean, readonlytrue
if the meta (Meta) key modifier is activated;
otherwise false
. On some platforms this attribute may
map to a differently-named key modifier.
shiftKey
of type boolean, readonlytrue
if the shift (Shift) key modifier is activated;
otherwise false
targetTouches
of type TouchList
, readonlyTouch
es for every point of contact that is touching
the surface and started on the element that is the
target of the current event.
touches
of type TouchList
, readonlyTouch
es for every point of contact currently
touching the surface.
initTouchEvent
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
type | DOMString | ✘ | ✘ | |
canBubble | boolean | ✘ | ✘ | |
cancelable | boolean | ✘ | ✘ | |
view | AbstractView | ✘ | ✘ | |
detail | long | ✘ | ✘ | |
ctrlKey | boolean | ✘ | ✘ | |
altKey | boolean | ✘ | ✘ | |
shiftKey | boolean | ✘ | ✘ | |
metaKey | boolean | ✘ | ✘ | |
touches |
| ✘ | ✘ | |
targetTouches |
| ✘ | ✘ | |
changedTouches |
| ✘ | ✘ |
void
This section is non-normative.
The examples below demonstrate the relations between the different
TouchList
members defined in a TouchEvent
.
TouchEvent
This example demonstrates the utility and relations between the
touches and targetTouches members defined in the TouchEvent
interface. The following code will generate different output based
on the number of touch points on the touchable element and the document:
<div id='touchable'> This element is touchable. </div> document.getElementById('touchable').addEventListener('touchstart', function(ev) { if (ev.touches.item(0) == ev.targetTouches.item(0)) { /** * If the first touch on the surface is also targeting the * "touchable" element, the code below should execute. * Since targetTouches is a subset of touches which covers the * entire surface, TouchEvent.touches >= TouchEvents.targetTouches * is always true. */ document.write('Hello Touch Events!'); } if (ev.touches.length == ev.targetTouches.length) { /** * If all of the active touch points are on the "touchable" * element, the length properties should be the same. */ document.write('All points are on target element') } if (ev.touches.length > 1) { /** * On a single touch input device, there can only be one point * of contact on the surface, so the following code can only * execute when the terminal supports multiple touches. */ document.write('Hello Multiple Touch!'); } }, false);
TouchEvent
This example demonstrates the utility of changedTouches and it's relation
with the other TouchList
members of the TouchEvent
interface.
The code is a example which triggers whenever a touch point is removed
from the defined touchable element:
<div id='touchable'> This element is touchable. </div> document.getElementById('touchable').addEventListener('touchend', function(ev) { /** * Example output when three touch points are on the surface, * two of them being on the "touchable" element and one point * in the "touchable" element is lifted from the surface: * * Touch points removed: 1 * Touch points left on element: 1 * Touch points left on document: 2 */ document.write('Removed: ' + ev.changedTouches.length); document.write('Remaining on element: ' + ev.targetTouches.length); document.write('Remaining on document: ' + ev.touches.length); }, false);
A user agent must dispatch this event type to indicate when the user places a touch point on the touch surface.
The target of this event must be an Element. If the touch point is within a frame, the event should be dispatched to an element in the child browsing context of that frame.
If the preventDefault method is called on this event, it should prevent any default actions caused by any touch events associated with the same active touch point, including mouse events or scrolling.
A user agent must dispatch this event type to indicate when the user removes a touch point from the touch surface, also including cases where the touch point physically leaves the touch surface, such as being dragged off of the screen.
The target of this event must be the same Element that received the touchstart event when this touch point was placed on the surface, even if the touch point has since moved outside the interactive area of the target element.
The touch point or points that were removed must be included
in the changedTouches attribute of the TouchEvent
, and
must not be included in the touches and targetTouches
attributes.
A user agent must dispatch this event type to indicate when the user moves a touch point along the touch surface.
The target of this event must be the same Element that received the touchstart event when this touch point was placed on the surface, even if the touch point has since moved outside the interactive area of the target element.
Note that the rate at which the user agent sends touchmove events is implementation-defined, and may depend on hardware capabilities and other implementation details.
If the preventDefault method is called on the first touchmove event of an active touch point, it should prevent any default action caused by any touchmove event associated with the same active touch point, such as scrolling.
A user agent must dispatch this event type to indicate when a touch
point has been disrupted in an implementation-specific manner, such as
a synchronous event or action originating from the UA canceling the
touch, or the touch point leaving the document window into a
non-document area which is capable of handling user interactions.
(e.g. The UA's native user interface, plug-ins) A user agent may
also dispatch this event type when the user places more touch
points on the touch surface than the device or implementation is
configured to store, in which case the earliest Touch
object
in the TouchList
should be removed.
DocumentTouch
Interface
The DocumentTouch
interface provides a mechanism by which the
user can create Touch
and TouchList
objects. The
DocumentTouch
interface must be implemented on the
Document object.
interface DocumentTouch {
Touch
createTouch (AbstractView view, EventTarget target, long identifier, long pageX, long pageY, long screenX, long screenY);
TouchList
createTouchList (Touch
[] touches);
TouchList
createTouchList (Touch
touch);
};
createTouch
Touch
object with the specified attributes.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
view | AbstractView | ✘ | ✘ | |
target | EventTarget | ✘ | ✘ | |
identifier | long | ✘ | ✘ | |
pageX | long | ✘ | ✘ | |
pageY | long | ✘ | ✘ | |
screenX | long | ✘ | ✘ | |
screenY | long | ✘ | ✘ |
Touch
createTouchList
TouchList
object containing the specified
Touch
objects.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
touches |
| ✘ | ✘ |
TouchList
createTouchList
TouchList
object containing a single Touch
.
Parameter | Type | Nullable | Optional | Description |
---|---|---|---|---|
touch |
| ✘ | ✘ |
TouchList
The user agent may dispatch both touch events and mouse events [DOM-LEVEL-2-EVENTS] in response to the same user input. If the user agent dispatches both touch events and mouse events in response to a single user action, then the touchstart event type must be dispatched before any mouse event types for that action. If the preventDefault method of touchstart or touchmove is called, the user agent should not dispatch any mouse event that would be a consequential result of the the prevented touch event.
If the user agent intreprets a sequence of touch events as a click, then it should dispatch mousemove, mousedown, mouseup, and click events (in that order) at the location of the touchend event for the corresponding touch input. If the contents of the document have changed during processing of the touch events, then the user agent may dispatch the mouse events to a different target than the touch events.
The default actions and ordering of any further touch and mouse events are implementation-defined, except as specified elsewhere.
This section is non-normative.
The working group maintains a list of open issues in this specification. These issues may be addressed in future revisions of the specification.
This section is non-normative.
Many thanks to the WebKit engineers for developing the model used as a basis for this spec, Neil Roberts (SitePen) for his summary of WebKit touch events, Peter-Paul Koch (PPK) for his write-ups and suggestions, Robin Berjon for developing the ReSpec.js spec authoring tool, and the WebEvents WG for their many contributions.
Many others have made additional comments as the spec developed, which have led to steady improvements. Among them are Matthew Schinckel, Andrew Grieve, and Cathy Chan. If I inadvertently omitted your name, please let me know.
No informative references.