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17.1.2 DOM Events

17.1.2 DOM Events

The DOM Level 3 Events specification has been under development by the W3C for about a decade. At the time of this writing, it has undergone substantial revision to bring it in line with current browser reality and it is finally in the “last call working draft” stage of standardization. It standardizes many of the legacy events described above and adds some new ones described here. These new event types are not yet widely supported, but browser vendors are expected to implement them once the standard is final.

As noted above, the DOM Level 3 Events specification standardizes the focusin and focusout events as bubbling alternatives to the focus and blur events and standardizes the mouseenter and mouseleave events as nonbubbling alternatives to mouseover and mouseout. This version of the standard also deprecates a number of event types that were defined by Level 2 but never widely implemented. Browsers are still allowed to generate events like DOMActivate, DOMFocusIn, and DOMNodeInserted, but these are no longer required, and they are not documented in this book.3

What is new in the DOM Level 3 Events specification is standardized support for two-dimensional mouse wheels via the wheel event and better support for text input events with a textinput event and with a new KeyboardEvent object that is passed as the argument to handlers for keydown, keyup, and keypress events.

A handler for a wheel event receives an event object with all the usual mouse event properties, and also deltaX, deltaY, and deltaZ properties that report rotation around three different mouse wheel axes. (Most mouse wheels are one or two dimensional and do not use deltaZ.) See §17.6 for more on mousewheel events.

DOM Level 3 Events defines the keypress event described above, but deprecates it in favor of a new event named textinput. Rather than a hard-to-use numeric keyCodevalue, the event object passed to a textinput event handler has a data property that specifies the string of text that was entered. The textinput event is not a keyboard-specific event: it is triggered whenever text input occurs, whether via the keyboard, cut-and-paste, drag-and-drop, and so on. The specification defines an inputMethod property on the event object and a set of constants representing different kinds of text input (keyboard, paste or drop, handwriting or voice recognition, and so on). At the time of this writing, Safari and Chrome support a version of this event using the mixed-case name textInput. Its event object includes the dataproperty but not the inputMethodproperty. §17.8 includes an example that makes use of this textInput event.

3. The only event in common use with “DOM” in its name is DOMContentLoaded. This event was introduced by Mozilla and was never part of the DOM Events standard.

17.1 Types of Events | 453

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