如何使用WAI-ARIA通知屏幕阅读器现在可以看到div

Question

How do you notify screen readers using WAI-ARIA that a div is now visible?

If we got the html

<div id="foo">Present main content</div>
<div id="bar" style="display: none;">Hidden content</div>

and then we

$('#foo').hide();
$('#bar').show();

how do we notify screen readers that they should notify the user about the now visible div (or possibly automatically focus on the now visible div)?

Answer 1

You do not need generally to tell screen readers that content is now visible. Use of aria-hidden makes no difference in practice, so I would suggest not using it. If you want the text content of the hidden div to be announced by a screen reader you may use role=alert or aria-live=polite (for example). You would use this for updated content that you want a screen reader to hear without having to move to the content location to discover it. For example a pop up message that does not receive focus, but contains text information that is relevant to a user after an action such as pressing a button.

update: I discussed with one of the people who developed ARIA 1.0, he suggested using HTML5 hidden instead of aria-hidden as a semantic indication that content is hidden. use it in conjunction with CSS display:none for older browsers. Browsers that support HTML5 hidden implement it using display:none in the user agent style sheet.

Answer 2

Tagging the content with role="alert" will cause it to fire an alert event which screen readers will respond to when it becomes visible:

<div id="content" role="alert">
...
</div>

$("#content").show();

This would alert the user when #content becomes visible.

aria-hidden should be used when there is something you want to hide from the screen reader, but show it to sighted users. Use with care however. See here for more: http://www.456bereastreet.com/archive/201205/hiding_visible_content_from_screen_readers_with_aria-hidden/

Answer 3

Use aria-hidden

Indicates that the element and all of its descendants are not visible or perceivable to any user as implemented by the author. See related aria-disabled.

If an element is only visible after some user action, authors MUST set the aria-hidden attribute to true. When the element is presented, authors MUST set the aria-hidden attribute to false or remove the attribute, indicating that the element is visible . Some assistive technologies access WAI-ARIA information directly through the DOM and not through platform accessibility supported by the browser. Authors MUST set aria-hidden="true" on content that is not displayed, regardless of the mechanism used to hide it. This allows assistive technologies or user agents to properly skip hidden elements in the document.

so your code could become

$('#foo').hide().attr('aria-hidden', 'true');
$('#bar').show().attr('aria-hidden', 'false');

Answer 4

I created a sample showing how you could using role="alert" to notify screen reader users when they are approaching the character limit of a textarea element, if you are trying to understand how to use the alert role, it may help:

There's more to it, but here's the small part of the code which produces the alert:

if (characterCount > myAlertTheshold) {
       var newAlert = document.createElement("div"); /* using the native js because it's faster */
       newAlert.setAttribute("role", "alert");
       newAlert.setAttribute("id", "alert");
       newAlert.setAttribute("class","sr-only");
       var msg = document.createTextNode('You have ' + charactersRemaining +' characters of ' + myMaxLength + ' left');
       newAlert.appendChild(msg);
       document.body.appendChild(newAlert);
     }

http://codepen.io/chris-hore/pen/emXovR