Add #annotations:group:GROUP_ID fragment parser

src/annotator/config/settings.js

@@ -102,6 +102,28 @@ function settingsFrom(window_) {
     return jsonConfigs.annotations || annotationsFromURL();
   }
 
+  /**
+   * Return the `#annotations:group:*` ID from the given URL's fragment.
+   *
+   * If the URL contains a `#annotations:group:<GROUP_ID>` fragment then return
+   * the group ID extracted from the fragment. Otherwise return `null`.
+   *
+   * @return {string|null} - The extracted ID, or null.
+   */
+  function group() {
+    function groupFromURL() {
+      const groupFragmentMatch = window_.location.href.match(
+        /#annotations:group:([A-Za-z0-9_-]+)$/
+      );
+      if (groupFragmentMatch) {
+        return groupFragmentMatch[1];
+      }
+      return null;
+    }
+
+    return jsonConfigs.group || groupFromURL();
+  }
+
   function showHighlights() {
     let showHighlights_ = hostPageSetting('showHighlights');
 
@@ -179,6 +201,9 @@ function settingsFrom(window_) {
     get clientUrl() {
       return clientUrl();
     },
+    get group() {
+      return group();
+    },
     get showHighlights() {
       return showHighlights();
     },

src/annotator/config/test/settings-test.js

@@ -289,6 +289,29 @@ describe('annotator.config.settingsFrom', function() {
     });
   });
 
+  [
+    {
+      description:
+        "returns an object with the group ID when there's a valid #annotations:group:<ID> fragment",
+      url: 'http://localhost:3000#annotations:group:alphanum3ric_-only',
+      returns: 'alphanum3ric_-only',
+    },
+    {
+      description: "returns null when there's a non-alphanumeric group ID",
+      url: 'http://localhost:3000#annotations:group:not%20alphanumeric',
+      returns: null,
+    },
+    {
+      description: "return null when there's an empty group ID",
+      url: 'http://localhost:3000#annotations:group:',
+      returns: null,
+    },
+  ].forEach(test => {
+    it(test.description, () => {
+      assert.deepEqual(settingsFrom(fakeWindow(test.url)).group, test.returns);
+    });
+  });
+
   describe('#query', function() {
     context(
       'when the host page has a js-hypothesis-config with a query setting',