Port tag suggestion service to JS

src/sidebar/tags.coffee

-module.exports = ['localStorage', (localStorage) ->
-  TAGS_LIST_KEY = 'hypothesis.user.tags.list'
-  TAGS_MAP_KEY = 'hypothesis.user.tags.map'
-
-  filter: (query) ->
-    savedTags = localStorage.getObject TAGS_LIST_KEY
-    savedTags ?= []
-
-    # Only show tags having query as a substring
-    filterFn = (e) ->
-      e.toLowerCase().indexOf(query.toLowerCase()) > -1
-
-    savedTags.filter(filterFn)
-
-  # Add newly added tags from an annotation to the stored ones and refresh
-  # timestamp for every tags used.
-  store: (tags) ->
-    savedTags = localStorage.getObject TAGS_MAP_KEY
-    savedTags ?= {}
-
-    for tag in tags
-      if savedTags[tag.text]?
-        # Update counter and timestamp
-        savedTags[tag.text].count += 1
-        savedTags[tag.text].updated = Date.now()
-      else
-        # Brand new tag, create an entry for it
-        savedTags[tag.text] = {
-          text: tag.text
-          count: 1
-          updated: Date.now()
-        }
-
-    localStorage.setObject TAGS_MAP_KEY, savedTags
-
-    tagsList = []
-    for tag of savedTags
-      tagsList[tagsList.length] = tag
-
-    # Now produce TAGS_LIST, ordered by (count desc, lexical asc)
-    compareFn = (t1, t2) ->
-      if savedTags[t1].count != savedTags[t2].count
-        return savedTags[t2].count - savedTags[t1].count
-      else
-        return -1 if t1 < t2
-        return 1 if t1 > t2
-        return 0
-
-    tagsList = tagsList.sort(compareFn)
-    localStorage.setObject TAGS_LIST_KEY, tagsList
-]

src/sidebar/tags.js

+'use strict';
+
+/**
+ * @typedef Tag
+ * @property {string} text - The label of the tag
+ * @property {number} count - The number of times this tag has been used.
+ * @property {number} updated - The timestamp when this tag was last used.
+ */
+
+/**
+ * Service for fetching tag suggestions and storing data to generate them.
+ *
+ * The `tags` service stores metadata about recently used tags to local storage
+ * and provides a `filter` method to fetch tags matching a query, ranked based
+ * on frequency of usage.
+ */
+// @ngInject
+function tags(localStorage) {
+  var TAGS_LIST_KEY = 'hypothesis.user.tags.list';
+  var TAGS_MAP_KEY = 'hypothesis.user.tags.map';
+
+  /**
+   * Return a list of tag suggestions matching `query`.
+   *
+   * @param {string} query
+   * @return {Tag[]} List of matching tags
+   */
+  function filter(query) {
+    var savedTags = localStorage.getObject(TAGS_LIST_KEY) || [];
+
+    return savedTags.filter((e) => {
+      return e.toLowerCase().indexOf(query.toLowerCase()) !== -1;
+    });
+  }
+
+  /**
+   * Update the list of stored tag suggestions based on the tags that a user has
+   * entered for a given annotation.
+   *
+   * @param {Tag} tags - List of tags.
+   */
+  function store(tags) {
+    // Update the stored (tag, frequency) map.
+    var savedTags = localStorage.getObject(TAGS_MAP_KEY) || {};
+    tags.forEach((tag) => {
+      if (savedTags[tag.text]) {
+        savedTags[tag.text].count += 1;
+        savedTags[tag.text].updated = Date.now();
+      } else {
+        savedTags[tag.text] = {
+          text: tag.text,
+          count: 1,
+          updated: Date.now(),
+        };
+      }
+    });
+    localStorage.setObject(TAGS_MAP_KEY, savedTags);
+
+    // Sort tag suggestions by frequency.
+    var tagsList = Object.keys(savedTags).sort((t1, t2) => {
+      if (savedTags[t1].count !== savedTags[t2].count) {
+        return savedTags[t2].count - savedTags[t1].count;
+      }
+      return t1.localeCompare(t2);
+    });
+    localStorage.setObject(TAGS_LIST_KEY, tagsList);
+  }
+
+  return {
+    filter,
+    store,
+  };
+}
+
+module.exports = tags;