Pointer Events

Much of today's web content assumes the user's pointing device will be a mouse. However, since many devices support other types of pointing
input devices, such as pen/stylus and touch surfaces, extensions to the
existing pointing device event models are needed. Pointer events address that need.

Pointer events are DOM events that are fired for a pointing device. They are designed to create a single DOM event model to handle pointing input devices such as a mouse, pen/stylus or touch (such as one or more fingers).

The pointer is a hardware-agnostic device that can target a specific set of screen coordinates. Having a single event model for pointers can simplify
creating Web sites and applications and provide a good user experience
regardless of the user's hardware. However, for scenarios when
device-specific handling is desired, pointer events defines a

pointerType property

to inspect the device type which produced the event.

The events needed to handle generic pointer input are analogous to

mouse events

(

mousedown

pointerdown

mousemove

pointermove

, etc.).

Consequently, pointer event types are intentionally similar to mouse event types.

Additionally, a pointer event contains the usual properties present
in mouse events (client coordinates, target element, button states,
etc.) in addition to new properties for other forms of input: pressure,
contact geometry, tilt, etc.

In fact, the

PointerEvent

interface inherits all of the

MouseEvent

properties, thus facilitating the migration of content from mouse events to pointer events.

Terminology

1. active buttons state

The condition when a pointer has a non-zero value for the

buttons

property. For example, in the case of a pen, when the pen has physical
contact with the digitizer, or at least one button is depressed while
hovering.

2. active pointer

Any pointer input device that can produce events. A pointer is considered active if it can still produce further events. For example, a pen that is a down state is considered active because it can produce additional events when the pen is lifted or moved.

3. digitizer

A sensing device with a surface that can detect contact. Most commonly, the sensing device is a touch-enabled screen that can sense input from an input device such as a pen, stylus, or finger. Some sensing devices can detect the close proximity of the input device, and the state is expressed as a hover following the mouse.

4. hit test

The process the browser uses to determine a target element for a pointer event. Typically, this is determined by considering the pointer's location and also the visual layout of elements in a document on screen media.

5. pointer

A hardware-agnostic representation of input devices that can target a specific coordinate (or set of coordinates) on a screen. Examples of pointer input devices are mouse, pen/stylus, and touch contacts.

6. pointer capture

Pointer capture allows the events for a pointer to be retargeted to a particular element other than the normal hit test result of the pointer's location.

7. pointer event

A DOM event fired for a pointer.

Interfaces

The primary interface is the

PointerEvent

interface which has a

constructor

plus several event types and associated global event handlers.

The standard also includes some extensions to the

Element

and

Navigator

interfaces.

The following sub-sections contain short descriptions of each interface and property.

PointerEvent interface

The

PointerEvent

interface extends the

MouseEvent

interface and has the following properties. (All of the following properties are Read only .)

pointerId

A unique identifier for the pointer causing the event.

width

The width (magnitude on the X axis), in CSS pixels, of the contact geometry of the pointer.

height

the height (magnitude on the Y axis), in CSS pixels, of the contact geometry of the pointer.

pressure

the normalized pressure of the pointer input in the range of

, where

and

represent the minimum and maximum pressure the hardware is capable of detecting, respectively.

tangentialPressure

The normalized tangential pressure of the pointer input (also known as barrel pressure or cylinder stress) in the range

1 to

, where

is the neutral position of the control.

tiltX

The plane angle (in degrees, in the range of

-90

) between the Y–Z plane and the plane containing both the pointer (e.g. pen stylus) axis and the Y axis.

tiltY

the plane angle (in degrees, in the range of

-90

) between the X–Z plane and the plane containing both the pointer (e.g. pen stylus) axis and the X axis.

twist

The clockwise rotation of the pointer (e.g. pen stylus) around its major axis in degrees, with a value in the range

pointerType

Indicates the device type that caused the event (mouse, pen, touch, etc.)

isPrimary

Indicates if the pointer represents the primary pointer of this pointer type.

Event types and Global Event Handlers

Pointer events have ten event types, seven of which have similar semantics to their mouse event counterparts (

down

up

move

over

out

enter

, and

leave

Below is a short description of each event type and its associated

Global Event Handler

1. Event:

pointerover

, Event Handler:

onpointerover

()

Fired when a pointer is moved into an element's hit test boundaries.

2. Event: pointerenter
, Event Handler:

onpointerenter()

Fired when a pointer is moved into the hit test boundaries of an element or one of its descendants, including as a result of a pointerdown event from a device that does not support hover (see

pointerdown

3. Event: pointerdown
, Event Handler:

onpointerdown

()

Fired when a pointer becomes active buttons state.

4. Event: pointermove, Event Handler:

onpointermove

()

Fired when a pointer changes coordinates. This event is also used if the change in pointer state can not be reported by other events.

5. Event: pointerup
, Event Handler:

onpointerup

()

Fired when a pointer is no longer active buttons state.

6. Event: pointercancel
, Event Handler:

onpointercancel

()

A browser fires this event if it concludes the pointer will no longer be able to generate events (for example the related device is deactived).

7. Event: pointerout
, Event Handler:

onpointerout

()

Fired for several reasons including: pointer is moved out of the hit test boundaries of an element; firing the pointerup event for a device that does not support hover (see pointerup); after firing the pointercancel event (see pointercancel); when a pen stylus leaves the hover range detectable by the digitizer.

8. Event: pointerleave
, Event Handler:

onpointerleave

()

Fired when a pointer is moved out of the hit test boundaries of an element. For pen devices, this event is fired when the stylus leaves the hover range detectable by the digitizer.

9. Event: gotpointercapture
, Event Handler:

ongotpointercapture

()

Fired when an element receives pointer capture.

10. Event: lostpointercapture
, Event Handler:

onlostpointercapture

()

Fired after pointer capture is released for a pointer.

Element extensions

There are three extensions to the

Element

interface:

setPointerCapture()

Designates a specific element as the capture target of future pointer events.

releasePointerCapture()

This method releases (stops) pointer capture that was previously set for a specific pointer event.

Navigator extension

The

Navigator.maxTouchPoints

property is used to determine the maximum number of simultaneous touch points that are supported at any single point in time.

Examples

This section contains examples of basic usage of using the pointer events interfaces.

Registering event handlers

This example registers a handler for every event type for the given element.

<html>
  <script>
    function over_handler(event) { }
    function enter_handler(event) { }
    function down_handler(event) { }
    function move_handler(event) { }
    function up_handler(event) { }
    function cancel_handler(event) { }
    function out_handler(event) { }
    function leave_handler(event) { }
    function gotcapture_handler(event) { }
    function lostcapture_handler(event) { }

    function init() {
      var el=document.getElementById("target");
      // Register pointer event handlers
      el.onpointerover = over_handler;
      el.onpointerenter = enter_handler;
      el.onpointerdown = down_handler;
      el.onpointermove = move_handler;
      el.onpointerup = up_handler;
      el.onpointercancel = cancel_handler;
      el.onpointerout = out_handler;
      el.onpointerleave = leave_handler;
      el.gotpointercapture = gotcapture_handler;
      el.lostpointercapture = lostcapture_handler;
    }
  </script>
  <body onload="init();">
    <div id="target"> Touch me ... </div>
  </body>
</html>

Event properties

This example illustrates accessing all of a touch event's properties.

<html>
  <script>
    var id = -1;

    function process_id(event) {
      // Process this event based on the event's identifier
    }
    function process_mouse(event) {
      // Process the mouse pointer event
    }
    function process_pen(event) {
      // Process the pen pointer event
    }
    function process_touch(event) {
      // Process the touch pointer event
    }
    function process_tilt(tiltX, tiltY) {
      // Tilt data handler
    }
    function process_pressure(pressure) {
      // Pressure handler
    }
    function process_non_primary(event) {
      // Non primary handler
    }

    function down_handler(ev) { 
      // Calculate the touch point's contact area
      var area = ev.width * ev.height;

      // Compare cached id with this event's id and process accordingly
      if (id == ev.identifier) process_id(ev);

      // Call the appropriate pointer type handler
      switch (ev.pointerType) {
        case "mouse": 
          process_mouse(ev); 
          break;
        case "pen": 
          process_pen(ev); 
          break;
        case "touch": 
          process_touch(ev); 
          break;
        default:
          console.log("pointerType " + ev.pointerType + " is Not suported");
      }

      // Call the tilt handler
      if (ev.tiltX != 0 && ev.tiltY != 0) process_tilt(ev.tiltX, ev.tiltY);

      // Call the pressure handler
      process_pressure(ev.pressure);

      // If this event is not primary, call the non primary handler
      if (!ev.isPrimary) process_non_primary(ev);
    }

    function init() {
      var el=document.getElementById("target");
      // Register pointerdown handler
      el.onpointerdown = down_handler;
    }
  </script>
  <body onload="init();">
    <div id="target"> Touch me ... </div>
  </body>
</html>

Determining the Primary Pointer

In some scenarios there may be multiple pointers (for example a device with both a touchscreen and a mouse) or a pointer supports multiple contact points (for example a touchscreen that supports multiple finger touches). The application can use the

isPrimary

property to identify a master pointer among the set of active pointers for each pointer type. If an application only wants to support a primary pointer, it can ignore all pointer events that are not primary.

For mouse there is only one pointer, so it will always be the primary pointer. For touch input, a pointer is considered primary if the user touched the screen when there were no other active touches.

For pen and stylus input, a pointer is considered primary if the user's pen initially contacted the screen when there were no other active pens contacting the screen.

Determining button states

Some pointer devices, such as mouse and pen, support multiple buttons and the button presses can be chorded i.e. depressing an additional button while another button on the pointer device is already depressed.

To determine the state of button presses, pointer events uses the

button

and

buttons

properties of the

MouseEvent

interface (that

PointerEvent

inherits from).

The following table provides the values of

button

and

buttons

for the various device button states.

Notice: The button property indicates a change in the state of the button. However, as in the case of touch, when multiple events occur with one event, all of them have the same value.

Pointer capture

Pointer capture allows events for a particular

pointer event

to be re-targeted to a particular element instead of the normal hit test at a pointer's location. This can be used to ensure that an element continues to receive pointer events even if the pointer device's contact moves off the element (for example by scrolling).

The following example shows pointer capture being set on an element.

<html>
<script>
  function downHandler(ev) {
    let el = document.getElementById("target");
    // Element 'target' will receive/capture further events
    el.setPointerCapture(ev.pointerId);
  }

  function init() {
    let el = document.getElementById("target");
    el.onpointerdown = downHandler;
  }
</script>
<body onload="init();">
  <div id="target"> Touch me ... </div>
</body>
</html>

The following example shows a pointer capture being released (when a

pointercancel

event occurs. The browser does this automatically when a

pointerup

pointercancel

event occurs.

<html>
  <script>
    function downHandler(ev) {
      let el = document.getElementById("target");
      // Element "target" will receive/capture further events
      el.setPointerCapture(ev.pointerId);
    }

    function cancelHandler(ev) {
      let el = document.getElementById("target");
      // Release the pointer capture
      el.releasePointerCapture(ev.pointerId);
    }

    function init() {
      let el = document.getElementById("target");
      // Register pointerdown and pointercancel handlers
      el.onpointerdown = downHandler;
      el.onpointercancel = cancelHandler;
    }
  </script>
  <body onload="init();">
    <div id="target"> Touch me ... </div>
  </body>
</html>

touch-action CSS property

The

touch-action

CSS property is used to specify whether or not the browser should apply its default (native) touch behavior (such as zooming or panning) to a region. This property may be applied to all elements except: non-replaced inline elements, table rows, row groups, table columns, and column groups.

A value of

auto

means the browser is free to apply its default touch behavior (to the specified region) and the value of

none

disables the browser's default touch behavior for the region. The values

pan-x

and

pan-y

, mean that touches that begin on the specified region are only for horizontal and vertical scrolling, respectively. The value

manipulation

means the browser may consider touches that begin on the element are only for scrolling and zooming.

In the following example, the browser's default touch behavior is disabled for the

div

element.

<html>
  <body>
    <div style="touch-action:none;">Can't touch this ... </div>
  </body>
</html>

In the following example, default touch behavior is disabled for some button elements.

button#tiny {
  touch-action: none;
}

In the following example, when the

target

element is touched, it will only pan in the horizontal direction.

#target {
  touch-action: pan-x;
}

Compatibility with mouse events

Although the pointer event interfaces enable applications to create enhanced user experiences on pointer enabled devices, the reality is the vast majority of today's web content is designed to only work with mouse input. Consequently, even if a browser supports pointer events, the browser must still process mouse events so content that assumes mouse-only input will work as is without direct modification.

Ideally, a pointer enabled application does not need to explicitly handle mouse input. However, because the browser must process mouse events, there may be some compatibility issues that need to be handled. This section contains information about pointer event and mouse event interaction and the ramifications for application developers.

The browser may map generic pointer input to mouse events for compatibility with mouse-based content. This mapping of events is called compatibility mouse events. Authors can prevent the production of certain compatibility mouse events by canceling the pointerdown event but note that:

Mouse events can only be prevented when the pointer is down.
Hovering pointers (e.g. a mouse with no buttons pressed) cannot have their mouse events prevented.
The
```
mouseover
```
,
```
mouseout
```
,
```
mouseenter
```
, and
```
mouseleave
```
events are never prevented (even if the pointer is down).

Best practices

Here are some best practices to consider when using pointer events:

Minimize the amount of work performed in event handlers.
Add the event handlers to a specific target element (rather than the entire document or nodes higher up in the document tree).
The target element (node) should be large enough to accommodate the largest contact surface area (typically a finger touch). If the target area is too small, touching it could result in firing other events for adjacent elements.

Implementation and deployment status

The pointer events browser compatibility data indicates pointer event support among desktop and mobile browsers is available almost everywhere except in Safari.

Some new value have been proposed for the

css touch-action

property as part of Pointer Events Level 2 specification but currently those new values have no implementation support.