- Spatial navigation and functional buttons
- Repeating key events
- Preventing default spatial navigation
Spatial navigation and functional buttons
Browsers based on the Vewd Core are generally designed to use the standard four-way directional keys on a remote control for spatial navigation. Vewd's spatial navigation works in a similar way to traditional TAB based keyboard access in most browsers, allowing users to move between focusable elements (links, form controls, image map areas). In addition, spatial navigation also employs heuristics that make arbitrary elements with attached
In most cases, websites can simply rely on Vewd's spatial navigation to handle site navigation. There are simple mechanisms to further [tweak spatial navigation for TV browsing](/tv/tweaking-spatial-navigation-for-tv-browsing/) using CSS3.
However, for maximum control, web authors may also choose to handle the navigation of their site (or specific aspects of their site, such as individual image carousel elements for instance) themselves by intercepting key presses from the remote control. This makes it possible to not only react to the basic directional buttons (UP, RIGHT, DOWN, LEFT), but to further bind functionality to the various shortcut and functional keys (such as BACK, INFO, OPTIONS or the RED button).
In previous versions of the Vewd Core, authors were encouraged to handle
keypress events. However, starting with the Vewd Core 3.4, Vewd is aligned with the DOM Level 3 Events model.
The most notable change here is that the
keypress event is now only fired for keys which produce a character value. From the list of functional buttons above, this means that only the number keys 0-9 and the ENTER (Confirm/Select/Ok) buttons can be detected via
Additionally, this specification deprecates the
keypress event, meaning that future versions of the specification – and, as a result, future versions of conformant browsers – should not fire this event anymore. For compatibility with existing content, it is unlikely that browsers will drop legacy support for this event, but we would still recommend using
keydown instead of
keypress going forward.
In the past, websites often handled key events by simply adding an
onkeydown property of the element or using
addEventListener. This automatically passes on the event object associated with the call, avoiding any ugly
Before the standardisation effort of DOM Level 3 Events, key handler functions would simply compare the
event.keyCode value to hardcoded values corresponding to specific keys. For instance, to detect if the UP arrow was pressed, the handler script would have been something like:
The potential problem with this approach has always been that the specific numerical values of
event.keyCode were never standardised – the same functional or navigation key, on different devices, may generate different key codes. For this reason, DOM Level 3 introduces a new, more abstracted method of identifying keys in the form of the DOM Level 3 Events Key values list and the new
event.key (as well as
event.char, which is however only applicable to keys which produce a character value).
Starting with the Vewd Core 3.4, the recommended method of identifying navigation and functional keys is therefore:
Although the DOM Level 3 Events model normatively uses
event.char, it still retains information on legacy key attributes such as
event.keyCode. For compatibility with existing content, it is likely that
event.keyCode will continue to be available for the time being.
To ensure backwards compatibility with previous Vewd Core versions, it may be necessary to combine the old and new way of comparing key events into a single expression:
Depending on the application, it is advisable not to include a large number of separate event handlers to various elements in the page, but to instead take advantage of event capture / bubbling and use an event delegation mechanism, hooking the
keydown handler on a top-level element (for instance, the
body) or object (
window or similar):
handler function, you may need to determine the element where the event originated. A reference to this can be easily obtained from the
Repeating key events
What happens when a user keeps a functional button on their remote control pressed is dependant on their specific device. Some devices will only send a single
keydown event until the button is released. Others may send a series of
keypress, if it's a key that produces a character value) and
keyupevents (as if the button was manually being pressed and released multiple times). Lastly, platforms that do support proper key repeats will send a continuous stream of
keypress, if it's a key that produces a character value) events, and only fire
keyup once the user releases the button.
In general, since it cannot be guaranteed that a device has full key repeat support, we'd recommend not making an application reliant on this behaviour.
If your applications does need to handle repeating / long-press button events, the switch to the DOM Level 3 Events model in the Vewd Core 3.4 may require some additional work in order to ensure backwards- and forwards-compatibility.
Previously, repeating keys (on supporting platforms) used to fire:
Starting with the Vewd Core 3.4, in accordance with the DOM Level 3 Events model, the browser will instead fire:
keyup(for keys that produce a character value)
keyup(for all other keys)
If for previous versions of the Vewd Core your code listened to repeating
keypress events, the best way to remain compatible is to register your handlers for both
keypress. To avoid having functionality being triggered twice (for the first button press in the old SDK, and for repeating character value keys in the new SDK), you can take advantage of the
event.repeat property introduced in DOM Level 3 Events to filter out unwanted duplicate events:
window.KeyboardEvent interface as an indicator for DOM 3 support, and only bind your event handler to either
Preventing default spatial navigation
When handling key events directly, you will probably want to stop the Vewd Core from carrying out its normal spatial navigation and element activation behaviours. This can simply be suppressed in the