WebAPI/BrowserAPI/KeyboardEvent

Dispatch KeyboardEvent across BrowserElements

This is a proposal to enable applications to handle/override the behavior of certain KeyboardEvent. For implementation, see bug 989198.

There are four scenarios which should be fulfilled:

Scenario	Description	Example Keys
SYSTEM-ONLY	For keys which should be handled by mozbrowser embedder iframe only.	'Power', 'DisplaySwap'
SYSTEM-FIRST	For keys which can be handled by mozbrowser embedder iframe first and can also be handled by mozbrowser embedded iframe then.	'Info', 'Settings'
APP-CANCELLED	For keys which should be handled by mozbrowser embedded iframe only.	'ColorF0Red', 'ColorF1Green', 'ColorF2Yellow', 'ColorF3Blue', 'ColorF4Grey'
APP-FIRST	For keys which keys can be handled by mozbrowser embedded iframe first and can also be handled by mozbrowser embedder iframe then.	'Info', 'Settings'

Note that some keys could be either SYSTEM-FIRST or APP-FIRST. The behavior is decided by the author of applications.

Proposal Concept

Four new events are proposed:

• mozbrowserbeforekeydown
• mozbrowserkeydown
• mozbrowserbeforekeyup
• mozbrowserkeyup

When a key is pressed down, the event sequence would be:

1. 'mozbrowserbeforekeydown' is dispatched to mozbrowser-embedder iframe
2. 'keydown' is dispatched to mozbrowser-embedded iframe
3. 'mozbrowserkeydown' is dispatched to mozbrowser-embedder iframe

Similarly, when a key is released, the event sequence would be:

1. 'mozbrowserbeforekeyup' is dispatched to mozbrowser-embedder iframe
2. 'keyup' is dispatched to mozbrowser-embedded iframe
3. 'mozbrowserkeyup' is dispatched to mozbrowser-embedder iframe

Nested mozbrowser iframes case

This proposal can be extended to nested mozbrowser iframes. The four new events will be dispatched to all mozbrowser-embedder iframes.

How to Fulfill Scenarios?

Here are some examples for each scenario.

Let's define some functions first.

function handleEvent(event) {
  dump("Receive event \'" + event.type + "\'.");
};

function handleEventAndPreventDefault(event) {
  dump("Receive event \'" + event.type + "\'.");
  event.preventDefault();
};

function checkAttrAndHandleEvent(event) {
  dump("Receive event \'" + event.type + "\' with embeddedCancelled equals to \'" + event.embeddedCancelled + "\'.");
  if (!event.embeddedCancelled) {
    // do something
  }
};

Scenario SYSTEM-ONLY

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', handleEventAndPreventDefault);
   window.addEventListener('mozbrowserbeforekeyup', handleEventAndPreventDefault);
   window.addEventListener('mozbrowserkeydown', function() { });
   window.addEventListener('mozbrowserkeyup', function() { });

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown		Receive event 'mozbrowserbeforekeydown'.
2	mozbrowserkeydown
3	mozbrowserbeforekeyup		Receive event 'mozbrowserbeforekeyup'.
4	mozbrowserkeyup

Scenario SYSTEM-FIRST

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', handleEvent);
   window.addEventListener('mozbrowserbeforekeyup', handleEvent);
   window.addEventListener('mozbrowserkeydown', function() { });
   window.addEventListener('mozbrowserkeyup', function() { });

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown		Receive event 'mozbrowserbeforekeydown'.
2		keydown	Receive event 'keydown'.
3	mozbrowserkeydown
4	mozbrowserbeforekeyup		Receive event 'mozbrowserbeforekeyup'.
5		keyup	Receive event 'keyup'.
6	mozbrowserkeyup

Scenario APP-CANCELLED

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', function() { });
   window.addEventListener('mozbrowserbeforekeyup', function() { });
   window.addEventListener('mozbrowserkeydown', checkAttrAndHandleEvent);
   window.addEventListener('mozbrowserkeyup', checkAttrAndHandleEvent);

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEventAndPreventDefault);
   window.addEventListener('keyup', handleEventAndPreventDefault);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown
2		keydown	Receive event 'keydown'.
3	mozbrowserkeydown		Receive event 'mozbrowserkeydown' with embeddedCancelled equals to 'true'.
4	mozbrowserbeforekeyup
5		keyup	Receive event 'keyup'.
6	mozbrowserup		Receive event 'mozbrowserkeyup' with embeddedCancelled equals to 'true'.

Scenario APP-FIRST

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', function() { });
   window.addEventListener('mozbrowserbeforekeyup', function() { });
   window.addEventListener('mozbrowserkeydown', checkAttrAndHandleEvent);
   window.addEventListener('mozbrowserkeyup', checkAttrAndHandleEvent);

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown
2		keydown	Receive event 'keydown'.
3	mozbrowserkeydown		Receive event 'mozbrowserkeyup' with embeddedCancelled equals to 'false'.
4	mozbrowserbeforekeyup
5		keyup	Receive event 'keyup'.
6	mozbrowserkeyup		Receive event 'mozbrowserkeyup' with embeddedCancelled equals to 'false'.

Proposal Details

mozbrowserbeforekeydown

Type	mozbrowserbeforekeydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	keydown event

keydown

Type	keydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	Set mozbrowserkeydown.embeddedCancelled to false; others defined in http://www.w3.org/TR/DOM-Level-3-Events/#event-type-keydown

mozbrowserkeydown

Type	mozbrowserkeydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	None

mozbrowserbeforekeyup

Type	mozbrowserbeforekeyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	keyup event

keyup

Type	keyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	Set mozbrowserkeyup.embeddedCancelled to false; others defined in http://www.w3.org/TR/DOM-Level-3-Events/#event-type-keyup

mozbrowserkeyup

Type	mozbrowserkeyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	None

Related Gaia Changes

Current Implementation

Currently, shell.js filters all hardware key event and wraps them in mozChromeEvent and then dispatch to Gaia System app. In Gaia System app, hardware_buttons.js listens for these low-level `mozChromeEvents`, processes them and generates higher-level events to handle autorepeat on the volume key long presses on Home and Sleep, and the Home+Sleep key combination. Other system app modules should listen for the high-level button events generated by this module.

The low level input events wrapped in mozChromeEvent are:

• home-button-press
• home-button-release
• sleep-button-press
• sleep-button-release
• volume-up-button-press
• volume-up-button-release
• volume-down-button-press
• volume-down-button-release

Hardware Buttons module (hardware_buttons.js) implements a state machine in it. Each state object has a mandatory `process()` method to process incoming low level input events and two optional `enter()` and `exit()` method when enter and exit state. Hardware Buttons module will listen to all low level input events and relay it to current state object to process. An all state transitions happen in `process()` or timer in `enter()` method.

Plan of Change

In patch of https://bugzilla.mozilla.org/show_bug.cgi?id=989198, Gina will keep both mozChromeEvents and new KeyboardEvents dispatching at the same time. But we only need to listen to one of them in Gaia.

Part 1

The state objects in hardware_buttons.js and software_button_manager.js all have dependency on low level input event names listed above. In this part, we stop listening to 'mozChromeEvent' and start listening to 'mozbrowserbeforekeydown' and mozbrowserbeforekeyup' event, and do a translation in handleEvent of hardware_buttons.js.

Translations are as follows:

Bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1014405

https://bugzilla.mozilla.org/show_bug.cgi?id=1014418