5.2.1.1 Attributes

detail of type long, readonly

Specifies some detail information about the Event, depending on the type of event.

The un-initialized value of this attribute MUST be 0.

view of type Window, readonly , nullable

The view attribute identifies the Window from which the event was generated.

The un-initialized value of this attribute MUST be null.

5.2.1.2 Dictionary UIEventInit Members

detail of type long, defaulting to 0

This value is initialized to a number that is application-specific.

view of type Window, nullable, defaulting to null

Should be initialized to the Window object of the global environment in which this event will be dispatched. If this event will be dispatched to an element, the view property should be set to the Window object containing the element's ownerDocument.

5.3.1.1 Attributes

relatedTarget of type EventTarget, readonly , nullable

Used to identify a secondary EventTarget related to a Focus event, depending on the type of event.

For security reasons with nested browsing contexts, when tabbing into or out of a nested context, the relevant EventTarget SHOULD be null.

The un-initialized value of this attribute MUST be null.

5.3.1.2 Dictionary FocusEventInit Members

relatedTarget of type EventTarget, nullable, defaulting to null

The relatedTarget should be initialized to the element whose bounds the mouse pointer just left (in the case of a mouseover or mouseenter event) or the element whose bounds the mouse pointer is entering (in the case of a mouseout or mouseleave or focusout event). For other events, this value need not be assigned (and will default to null).

5.4.1.1 Attributes

altKey of type boolean, readonly

Refer to the KeyboardEvent.altKey attribute.

The un-initialized value of this attribute MUST be false.

button of type short, readonly

During mouse events caused by the depression or release of a mouse button, button MUST be used to indicate which pointer device button changed state.

The value of the MouseEvent.button attribute MUST be as follows:

• 0 MUST indicate the primary button of the device (in general, the left button or the only button on single-button devices, used to activate a user interface control or select text) or the un-initialized value.
• 1 MUST indicate the auxiliary button (in general, the middle button, often combined with a mouse wheel).
• 2 MUST indicate the secondary button (in general, the right button, often used to display a context menu).

Some pointing devices provide or simulate more button states, and values higher than 2 or lower than 0 MAY be used to represent such buttons.

Note

Note: The value of button is not updated for events not caused by the depression/release of a mouse button. In these scenarios, take care not to interpret the value 0 as the left button, but rather as the un-initialized value.

Note

Authoring Note: Some default actions related to events such as mousedown and mouseup depend on the specific mouse button in use.

The un-initialized value of this attribute MUST be 0.

buttons of type unsigned short, readonly

During any mouse events, buttons MUST be used to indicate which combination of mouse buttons are currently being pressed, expressed as a bitmask.

Note

Note: Though similarly named, the values for the buttons attribute and the button attribute are very different. The value of button is assumed to be valid during mousedown / mouseup event handlers, whereas the buttons attribute reflects the state of the mouse's buttons for any trusted MouseEvent object (while it is being dispatched), because it can represent the "no button currently active" state (0).

The value of the MouseEvent.buttons attribute MUST be as follows:

• 0 MUST indicate no button is currently active.
• 1 MUST indicate the primary button of the device (in general, the left button or the only button on single-button devices, used to activate a user interface control or select text).
• 2 MUST indicate the secondary button (in general, the right button, often used to display a context menu), if present.
• 4 MUST indicate the auxiliary button (in general, the middle button, often combined with a mouse wheel).

Some pointing devices provide or simulate more buttons. To represent such buttons, the value MUST be doubled for each successive button (in the binary series 8, 16, 32, ... ).

Note

Note: Because the sum of any set of button values is a unique number, a content author can use a bitwise operation to determine how many buttons are currently being pressed and which buttons they are, for an arbitrary number of mouse buttons on a device. For example, the value 3 indicates that the left and right button are currently both pressed, while the value 5 indicates that the left and middle button are currently both pressed.

Note

Authoring Note: Some default actions related to events such as mousedown and mouseup depend on the specific mouse button in use.

The un-initialized value of this attribute MUST be 0.

clientX of type long, readonly

The horizontal coordinate at which the event occurred relative to the viewport associated with the event.

The un-initialized value of this attribute MUST be 0.

clientY of type long, readonly

The vertical coordinate at which the event occurred relative to the viewport associated with the event.

The un-initialized value of this attribute MUST be 0.

ctrlKey of type boolean, readonly

Refer to the KeyboardEvent.ctrlKey attribute.

The un-initialized value of this attribute MUST be false.

metaKey of type boolean, readonly

Refer to the KeyboardEvent.metaKey attribute.

The un-initialized value of this attribute MUST be false.

relatedTarget of type EventTarget, readonly , nullable

Used to identify a secondary EventTarget related to a UI event, depending on the type of event.

The un-initialized value of this attribute MUST be null.

screenX of type long, readonly

The horizontal coordinate at which the event occurred relative to the origin of the screen coordinate system.

The un-initialized value of this attribute MUST be 0.

screenY of type long, readonly

The vertical coordinate at which the event occurred relative to the origin of the screen coordinate system.

The un-initialized value of this attribute MUST be 0.

shiftKey of type boolean, readonly

Refer to the KeyboardEvent.shiftKey attribute.

The un-initialized value of this attribute MUST be false.

5.4.1.2 Methods

getModifierState

Introduced in this specification

Queries the state of a modifier using a key value. See Modifier keys for a list of valid (case-sensitive) arguments to this method.

Returns true if it is a modifier key and the modifier is activated, false otherwise.

Parameter	Type	Nullable	Optional	Description
keyArg	DOMString	✘	✘	Refer to the KeyboardEvent.getModifierState() method for a description of this parameter.

Return type: boolean

5.4.1.3 Dictionary MouseEventInit Members

button of type short, defaulting to 0

Initializes the button attribute of the MouseEvent object to a number representing the desired state of the button(s) of the mouse.

Note

Note: The value 0 is used to represent the primary mouse button, 1 is used to represent the auxiliary/middle mouse button, and 2 to represent the right mouse button. Numbers greater than 2 are also possible, but are not specified in this document.

buttons of type unsigned short, defaulting to 0

Initializes the buttons attribute of the MouseEvent object to a number representing one or more of the button(s) of the mouse that are to be considered active.

Note

Note: The buttons attribute is a bit-field. If a mask value of 1 is true when applied to the value of the bit field, then the primary mouse button is down. If a mask value of 2 is true when applied to the value of the bit field, then the right mouse button is down. If a mask value of 4 is true when applied to the value of the bit field, then the auxiliary/middle button is down.

In JavaScript, to initialize the buttons attribute as if the right (2) and middle button (4) were being pressed simultaneously, the buttons value can be assigned as either:
{ buttons: 2 | 4 }
or:
{ buttons: 6 }

clientX of type long, defaulting to 0

See clientY (substituting "horizontal" for "vertical").

clientY of type long, defaulting to 0

Initializes the clientY attribute of the MouseEvent object to the desired vertical position of the mouse pointer relative to the client window of the user's browser.

Initializing the event object to the given mouse position must not move the user's mouse pointer to the initialized position.

relatedTarget of type EventTarget, nullable, defaulting to null

The relatedTarget should be initialized to the element whose bounds the mouse pointer just left (in the case of a mouseover or mouseenter event) or the element whose bounds the mouse pointer is entering (in the case of a mouseout or mouseleave or focusout event). For other events, this value need not be assigned (and will default to null).

screenX of type long, defaulting to 0

See screenY (substituting "horizontal" for "veritcal").

screenY of type long, defaulting to 0

Initializes the screenY attribute of the MouseEvent object to the desired vertical relative position of the mouse pointer on the user's screen.

Initializing the event object to the given mouse position must not move the user's mouse pointer to the initialized position.

5.4.2.1 Dictionary EventModifierInit Members

altKey of type boolean, defaulting to false

Initializes the altKey attribute of the MouseEvent or KeyboardEvent objects to true if the 'Alt' (alternative) (or 'Option') key modifier is to be considered active, false otherwise.

When true, implementations must also initialize the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Alt' must return true.

ctrlKey of type boolean, defaulting to false

Initializes the altKey attribute of the MouseEvent or KeyboardEvent objects to true if the 'Control' (control) key modifier is to be considered active, false otherwise.

When true, implementations must also initialize the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with either the parameter 'Control' or the parameter 'Accel' must return true.

metaKey of type boolean, defaulting to false

Initializes the metaKey attribute of the MouseEvent or KeyboardEvent objects to true if the 'Meta' key modifier is to be considered active, false otherwise.

When true, implementations must also initialize the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with either the parameter 'Meta' or the parameter 'Accel' must return true.

modifierAltGraph of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'AltGraph' must return true.

modifierCapsLock of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'CapsLock' must return true.

modifierFn of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Fn' must return true.

modifierFnLock of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'FnLock' must return true.

modifierHyper of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Hyper' must return true.

modifierNumLock of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'NumLock' must return true.

modifierOS of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'OS' must return true.

modifierScrollLock of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'ScrollLock' must return true.

modifierSuper of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Super' must return true.

modifierSymbol of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Symbol' must return true.

modifierSymbolLock of type boolean, defaulting to false

Initializes the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'SymbolLock' must return true.

shiftKey of type boolean, defaulting to false

Initializes the shiftKey attribute of the MouseEvent or KeyboardEvent objects to true if the 'Shift' key modifier is to be considered active, false otherwise.

When true, implementations must also initialize the event object's key modifier state such that calls to the MouseEvent.getModifierState() or KeyboardEvent.getModifierState() when provided with the parameter 'Shift' must return true.

5.5.1.1 Attributes

deltaMode of type unsigned long, readonly

The deltaMode attribute contains an indication of the units of measurement for the delta values. The default value is DOM_DELTA_PIXEL (pixels).

This attribute MUST be set to one of the DOM_DELTA constants to indicate the units of measurement for the delta values. The precise measurement is specific to device, operating system, and application configurations.

The un-initialized value of this attribute MUST be 0.

deltaX of type double, readonly

In user agents where the default action of the wheel event is to scroll, the value MUST be the measurement along the x-axis (in pixels, lines, or pages) to be scrolled in the case where the event is not cancelled. Otherwise, this is an implementation-specific measurement (in pixels, lines, or pages) of the movement of a wheel device around the x-axis.

The un-initialized value of this attribute MUST be 0.0.

deltaY of type double, readonly

In user agents where the default action of the wheel event is to scroll, the value MUST be the measurement along the y-axis (in pixels, lines, or pages) to be scrolled in the case where the event is not cancelled. Otherwise, this is an implementation-specific measurement (in pixels, lines, or pages) of the movement of a wheel device around the y-axis.

The un-initialized value of this attribute MUST be 0.0.

deltaZ of type double, readonly

In user agents where the default action of the wheel event is to scroll, the value MUST be the measurement along the z-axis (in pixels, lines, or pages) to be scrolled in the case where the event is not cancelled. Otherwise, this is an implementation-specific measurement (in pixels, lines, or pages) of the movement of a wheel device around the z-axis.

The un-initialized value of this attribute MUST be 0.0.

5.5.1.2 Constants

DOM_DELTA_LINE of type unsigned long

The units of measurement for the delta MUST be individual lines of text. This is the case for many form controls.

DOM_DELTA_PAGE of type unsigned long

The units of measurement for the delta MUST be pages, either defined as a single screen or as a demarcated page.

DOM_DELTA_PIXEL of type unsigned long

The units of measurement for the delta MUST be pixels. This is the most typical case in most operating system and implementation configurations.

5.5.1.3 Dictionary WheelEventInit Members

deltaMode of type unsigned long, defaulting to 0

Initializes the deltaMode attribute on the WheelEvent object to the enumerated values 0, 1, or 2, which represent the amount of pixels scrolled (DOM_DELTA_PIXEL), lines scrolled (DOM_DELTA_LINE), or pages scrolled (DOM_DELTA_PAGE) if the rotation of the wheel would have resulted in scrolling.

deltaX of type double, defaulting to 0.0

See deltaZ attribute.

deltaY of type double, defaulting to 0.0

See deltaZ attribute.

deltaZ of type double, defaulting to 0.0

Initializes the deltaZ attribute of the WheelEvent object. Relative positive values for this attribute (as well as the deltaX and deltaY attributes) are given by a right-hand coordinate system where the X, Y, and Z axes are directed towards the right-most edge, bottom-most edge, and farthest depth (away from the user) of the document, respectively. Negative relative values are in the respective opposite directions.

5.6.1.1 Attributes

altKey of type boolean, readonly

true if the 'Alt' (alternative) (or 'Option') key modifier was active.

The un-initialized value of this attribute MUST be false.

code of type DOMString, readonly

code holds a string that identifies the physical key being pressed. The value is not affected by the current keyboard layout or modifier state, so a particular key will always return the same value.

The un-initialized value of this attribute MUST be "" (the empty string).

ctrlKey of type boolean, readonly

true if the 'Control' (control) key modifier was active.

The un-initialized value of this attribute MUST be false.

isComposing of type boolean, readonly

true if the key event occurs as part of a composition session, i.e., after a compositionstart event and before the corresponding compositionend event.

The un-initialized value of this attribute MUST be false.

key of type DOMString, readonly

key holds the key value of the key pressed. If the value is has a printed representation, it MUST be a non-empty Unicode character string, conforming to the algorithm for determining the key value defined in this specification. If the value is a control key which has no printed representation, it MUST be one of the key values defined in the key values set, as determined by the algorithm for determining the key value. Implementations that are unable to identify a key MUST use the key value 'Unidentified'.

Note

Note: The key attribute is not related to the legacy keyCode attribute and does not have the same set of values.

The un-initialized value of this attribute MUST be "" (the empty string).

location of type unsigned long, readonly

The location attribute contains an indication of the logical location of the key on the device.

This attribute MUST be set to one of the DOM_KEY_LOCATION constants to indicate the location of a key on the device.

If a user agent allows keys to be remapped, then the location value for a remapped key MUST be set to a value which is appropriate for the new key. For example, if the ControlLeft key is mapped to the KeyQ key, then the location attribute MUST be set to DOM_KEY_LOCATION_STANDARD. Conversely, if the KeyQ key is remapped to Control, then the location attribute MUST be set to either DOM_KEY_LOCATION_LEFT or DOM_KEY_LOCATION_RIGHT.

The un-initialized value of this attribute MUST be 0.

metaKey of type boolean, readonly

true if the meta ('Meta') key modifier was active.

Note

Note: The 'Command' ('⌘') key modifier on Macintosh systems is represented using this key modifier.

The un-initialized value of this attribute MUST be false.

repeat of type boolean, readonly

true if the key has been pressed in a sustained manner. Holding down a key MUST result in the repeating the events keydown, beforeedit, edit in this order, at a rate determined by the system configuration. For mobile devices which have long-key-press behavior, the first key event with a repeat attribute value of 'true' MUST serve as an indication of a long-key-press. The length of time that the key MUST be pressed in order to begin repeating is configuration-dependent.

The un-initialized value of this attribute MUST be false.

shiftKey of type boolean, readonly

true if the shift ('Shift') key modifier was active.

The un-initialized value of this attribute MUST be false.

5.6.1.2 Methods

getModifierState

Queries the state of a modifier using a key value. See Modifier keys for a list of valid (case-sensitive) arguments to this method.

Parameter	Type	Nullable	Optional	Description
keyArg	DOMString	✘	✘	A modifier key value. Valid modifier keys are defined in the Modifier Keys table in [DOM3 key Values]. Returns true if it is a modifier key and the modifier is activated, false otherwise. Note Note: If an application wishes to distinguish between right and left modifiers, this information could be deduced using keyboard events and KeyboardEvent.location.

Return type: boolean

5.6.1.3 Constants

DOM_KEY_LOCATION_LEFT of type unsigned long

The key activated originated from the left key location (when there is more than one possible location for this key).

The left 'Control' key on a PC 101 Key US keyboard.

DOM_KEY_LOCATION_NUMPAD of type unsigned long

The key activation originated on the numeric keypad or with a virtual key corresponding to the numeric keypad (when there is more than one possible location for this key). Note that the 'NumLock' key should always be encoded with a location of DOM_KEY_LOCATION_STANDARD.

The '1' key on a PC 101 Key US keyboard located on the numeric pad.

DOM_KEY_LOCATION_RIGHT of type unsigned long

The key activation originated from the right key location (when there is more than one possible location for this key).

The right 'Shift' key on a PC 101 Key US keyboard.

DOM_KEY_LOCATION_STANDARD of type unsigned long

The key activation MUST NOT be distinguished as the left or right version of the key, and (other than the 'NumLock' key) did not originate from the numeric keypad (or did not originate with a virtual key corresponding to the numeric keypad).

The 'Q' key on a PC 101 Key US keyboard.

The 'NumLock' key on a PC 101 Key US keyboard.

The '1' key on a PC 101 Key US keyboard located in the main section of the keyboard.

5.6.1.4 Dictionary KeyboardEventInit Members

code of type DOMString, defaulting to ""

Initializes the code attribute of the KeyboardEvent object to the unicode character string representing the key that was pressed, ignoring any keyboard modifications such as keyboard layout. This value should be one of the code values defined in [DOM3 code Values].

isComposing of type boolean, defaulting to false

Initializes the isComposing attribute of the KeyboardEvent object. This attribute should be set to true if the event being constructed occurs as part of a composition sequence, false otherwise.

key of type DOMString, defaulting to ""

Initializes the key attribute of the KeyboardEvent object to the unicode character string representing the meaning of a key after taking into account all keyboard modifications (such as shift-state). This value is the final effective value of the key. If the key is not a printable character, then it should be one of the key values defined in [DOM3 key Values].

location of type unsigned long, defaulting to 0

Initializes the location attribute of the KeyboardEvent object to one of the following location numerical constants:

• KeyboardEvent.DOM_KEY_LOCATION_STANDARD (numerical value 0)
• KeyboardEvent.DOM_KEY_LOCATION_LEFT (numerical value 1)
• KeyboardEvent.DOM_KEY_LOCATION_RIGHT (numerical value 2)
• KeyboardEvent.DOM_KEY_LOCATION_NUMPAD (numerical value 3)

repeat of type boolean, defaulting to false

Initializes the repeat attribute of the KeyboardEvent object. This attribute should be set to true if the the current KeyboardEvent is considered part of a repeating sequence of similar events caused by the long depression of any single key, false otherwise.

5.7.1.1 Attributes

data of type DOMString, readonly

data holds the value of the characters generated by an input method. This MAY be a single Unicode character or a non-empty sequence of Unicode characters [Unicode]. Characters SHOULD be normalized as defined by the Unicode normalization form NFC, defined in [UAX #15]. This attribute MAY be the empty string.

The un-initialized value of this attribute MUST be "" (the empty string).

5.7.1.2 Dictionary CompositionEventInit Members

data of type DOMString, defaulting to ""

Initializes the data attribute of the CompositionEvent object to the characters generated by the IME composition.

5.7.5.1 Including Key Events During Composition

If a user agent does not suppress these events during composition, then it MUST set the key event's isComposing attribute to true for any events that occur during a composition session.

5.7.5.2 Suppressing Key Events During Composition

If key events are suppressed between compositionstart and compositionend, then the first or last key pressed might result in unmatched keydown and keyup events. If a user agent suppresses key events during composition, then it MUST ensure that all keydown and keyup events occur in matching pairs.

To ensure that the initial keydown has a matching keyup, a user agent might insert an extra keyup to match the keydown that initiated a composition session, as shown in the following example:

To ensure that the composition session doesn't end with a dangling keyup event, a user agent can choose either (A) to suppress this keyup event, or (B) to insert an extra keydown event.

An example event sequence where both the keydown and keyup events have been suppressed:

An example event sequence where a keydown has been inserted: