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Technique SCR20:Using both keyboard and other device-specific functions

Applicability

Applies to all content that uses Script to implement functionality.

This technique relates to 2.1.1: Keyboard (Sufficient when used with G90: Providing keyboard-triggered event handlers).

Description

The objective of this technique is to illustrate the use of both keyboard-specific and mouse-specific events with code that has a scripting function associated with an event. Using both keyboard-specific and mouse-specific events together ensures that content can be operated by a wide range of devices. For example, a script may perform the same action when a keypress is detected that is performed when a mouse button is clicked. This technique goes beyond the Success Criterion requirement for keyboard access by including not only keyboard access but access using other devices as well.

In JavaScript, commonly used event handlers include, onblur, onchange, onclick, ondblclick, onfocus, onkeydown, onkeypress, onkeyup, onload, onmousedown, onmousemove, onmouseout, onmouseover, onmouseup, onreset, onselect, onsubmit, onunload. Some mouse-specific functions have a logical corresponding keyboard-specific function (such as 'onmouseover' and 'onfocus'). A keyboard event handler should be provided that executes the same function as the mouse event handler.

The following table suggests keyboard event handlers to pair mouse event handlers.

Device Handler Correspondences
Use... ...with
mousedown keydown
mouseup keyup
click [1] keypress [2]
mouseover focus
mouseout blur

1 Although click is in principle a mouse event handler, most HTML user agents also process this event when a native HTML control (e.g. a button or a link) is activated, regardless of whether it was activated with the mouse or the keyboard. In practice, therefore, it is not necessary to duplicate this event when adding handlers to natively focusable HTML elements. However, it is necessary when adding handlers to other events, such as in Example 2 below.

2 Since the keypress event handler reacts to any key, the event handler function should check first to ensure the Enter key was pressed before proceeding to handle the event. Otherwise, the event handler will run each time the user presses any key, even the tab key to leave the control, and this is usually not desirable.

Some mouse-specific functions (such as dblclick and mousemove) do not have a corresponding keyboard-specific function. This means that some functions may need to be implemented differently for each device (for example, including a series of buttons to execute, via keyboard, the equivalent mouse-specific functions implemented).

Examples

Example 1

In this example of an image link, the image is changed when the user positions the pointer over the image. To provide keyboard users with a similar experience, the image is also changed when the user tabs to it. 

<a href="menu.php" onmouseover="swapImageOn('menu')" onfocus="swapImageOn('menu')" 
   onmouseout="swapImageOff('menu')" onblur="swapImageOff('menu')"> 
   <img id="menu" src="menu_off.gif" alt="Menu"> 
</a>

Example 2

This example shows a custom link control where both the mouse and the keyboard can be used to activate the function. The mouse onclick event is duplicated by an appropriate keyboard onkeypress event. The tabindex attribute ensures that the keyboard will have a tab stop on the span element. Note that in this example, the nextPage() function should check that the key pressed was Enter, otherwise it will respond to all keyboard actions while the span has focus, which is not the desired behavior. 

<span onclick="nextPage();" onkeypress="nextPage();" role="link" tabindex="0">
  <img alt="Go to next page" src="arrow.gif">
</span>

Other sources

No endorsement implied.

Tests

Procedure

  1. Find all interactive functionality
  2. Check that all interactive functionality can be accessed using the keyboard alone

Expected Results

  • #2 is true
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