comparison core/misc/announce.es6.js @ 0:c75dbcec494b

Initial commit from drush-created site

+/**
+ * @file
+ * Adds an HTML element and method to trigger audio UAs to read system messages.
+ *
+ * Use {@link Drupal.announce} to indicate to screen reader users that an
+ * element on the page has changed state. For instance, if clicking a link
+ * loads 10 more items into a list, one might announce the change like this.
+ *
+ * @example
+ * $('#search-list')
+ *   .on('itemInsert', function (event, data) {
+ *     // Insert the new items.
+ *     $(data.container.el).append(data.items.el);
+ *     // Announce the change to the page contents.
+ *     Drupal.announce(Drupal.t('@count items added to @container',
+ *       {'@count': data.items.length, '@container': data.container.title}
+ *     ));
+ *   });
+ */
+
+(function (Drupal, debounce) {
+  let liveElement;
+  const announcements = [];
+
+  /**
+   * Builds a div element with the aria-live attribute and add it to the DOM.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the behavior for drupalAnnouce.
+   */
+  Drupal.behaviors.drupalAnnounce = {
+    attach(context) {
+      // Create only one aria-live element.
+      if (!liveElement) {
+        liveElement = document.createElement('div');
+        liveElement.id = 'drupal-live-announce';
+        liveElement.className = 'visually-hidden';
+        liveElement.setAttribute('aria-live', 'polite');
+        liveElement.setAttribute('aria-busy', 'false');
+        document.body.appendChild(liveElement);
+      }
+    },
+  };
+
+  /**
+   * Concatenates announcements to a single string; appends to the live region.
+   */
+  function announce() {
+    const text = [];
+    let priority = 'polite';
+    let announcement;
+
+    // Create an array of announcement strings to be joined and appended to the
+    // aria live region.
+    const il = announcements.length;
+    for (let i = 0; i < il; i++) {
+      announcement = announcements.pop();
+      text.unshift(announcement.text);
+      // If any of the announcements has a priority of assertive then the group
+      // of joined announcements will have this priority.
+      if (announcement.priority === 'assertive') {
+        priority = 'assertive';
+      }
+    }
+
+    if (text.length) {
+      // Clear the liveElement so that repeated strings will be read.
+      liveElement.innerHTML = '';
+      // Set the busy state to true until the node changes are complete.
+      liveElement.setAttribute('aria-busy', 'true');
+      // Set the priority to assertive, or default to polite.
+      liveElement.setAttribute('aria-live', priority);
+      // Print the text to the live region. Text should be run through
+      // Drupal.t() before being passed to Drupal.announce().
+      liveElement.innerHTML = text.join('\n');
+      // The live text area is updated. Allow the AT to announce the text.
+      liveElement.setAttribute('aria-busy', 'false');
+    }
+  }
+
+  /**
+   * Triggers audio UAs to read the supplied text.
+   *
+   * The aria-live region will only read the text that currently populates its
+   * text node. Replacing text quickly in rapid calls to announce results in
+   * only the text from the most recent call to {@link Drupal.announce} being
+   * read. By wrapping the call to announce in a debounce function, we allow for
+   * time for multiple calls to {@link Drupal.announce} to queue up their
+   * messages. These messages are then joined and append to the aria-live region
+   * as one text node.
+   *
+   * @param {string} text
+   *   A string to be read by the UA.
+   * @param {string} [priority='polite']
+   *   A string to indicate the priority of the message. Can be either
+   *   'polite' or 'assertive'.
+   *
+   * @return {function}
+   *   The return of the call to debounce.
+   *
+   * @see http://www.w3.org/WAI/PF/aria-practices/#liveprops
+   */
+  Drupal.announce = function (text, priority) {
+    // Save the text and priority into a closure variable. Multiple simultaneous
+    // announcements will be concatenated and read in sequence.
+    announcements.push({
+      text,
+      priority,
+    });
+    // Immediately invoke the function that debounce returns. 200 ms is right at
+    // the cusp where humans notice a pause, so we will wait
+    // at most this much time before the set of queued announcements is read.
+    return (debounce(announce, 200)());
+  };
+}(Drupal, Drupal.debounce));