Notes

Alerts are dynamic content that is injected into the page when it changes and a person using a screenreader needs to know that some state of the application has changed.

  • Use alerts sparingly.
  • If an alert is present on page load, it won’t be read automatically
    • If an element is present on page load, it is not technically an alert
  • The alert will be read by the screen reader when it becomes visible / appears in the DOM

Code examples

<label for="favorite-letter">
  What is your favorite NATO letter?
  <span>Required</span>
</label>

<input type="text"
       id="favorite-letter"
       aria-describedby="favorite-error favorite-hint"
       required>

<div role="alert" class="alert inert">
  <!--- Do not reference this alert element
        directly with aria-describedby -->
  <div id="favorite-error">
    <!--- Use JS to inject the alert here -->
  </div>     
</div>

<div class="hint" id="favorite-hint">
  Example: Alpha, Bravo, Charlie
</div>

<button id="show-error">
  Toggle error
</button>
Example: Alpha, Bravo, Charlie

Developer notes

Browser + screenreader quirks

  • Screenreaders do not implement alerts uniformly and must be tested
    • Just because an alert pattern works in one screenreader doesn’t mean it will work in all three
  • The element referenced by the aria-describedby attribute cannot use the role="alert" attribute (see example above for workaround).
  • NVDA will read the alert twice if it appears while the input is in focus: once from the role="alert" being injected and from the aria-describedby association.
  • NVDA needs a fraction of a second to catch up with changes in the DOM, use a setTimeout to delay displaying the alert

Name

  • Inner text describes alert when it appears on screen

Role

  • Use role="alert" for elements injected into the page

Focus

  • Focus does move to the element when the alert appears