Fix Uncaught TypeError on notes emails subscribe

See #298

app/assets/javascripts/bp_notes.js

@@ -357,10 +357,17 @@ function subscribeToNotes(button) {
       var subbedVal = (isSubbed == "true") ? "false" : "true";
       jQuery("a.subscribe_to_notes").attr("data-bp_is_subbed", subbedVal);
 
-      // Change button text
-      var txt = jQuery("a.subscribe_to_notes span.ui-button-text").html();
-      var newButtonText = txt.match("Unsubscribe") ? txt.replace("Unsubscribe", "Subscribe") : txt.replace("Subscribe", "Unsubscribe");
-      jQuery("a.subscribe_to_notes span.ui-button-text").html(newButtonText);
+      /*
+       * Update link text.
+       * Note that there are two links that allow users to subscribe/unsubscribe from notes emails. Given any ontology,
+       * one link is located on the top-level Notes tab, and the other link is located on the Notes sub-tab on the
+       * right-hand side of the Classes tab. Both links are handled by the subscriptions controller, and the text of
+       * both should be updated on success.
+       */
+      const matches = document.querySelectorAll('a.subscribe_to_notes');
+      matches.forEach(match => {
+        match.textContent = (subbedVal === 'true') ? 'Unsubscribe from notes emails' : 'Subscribe to notes emails';
+      });
     },
     error: function(data) {
       jQuery(".notes_subscribe_spinner").hide();

app/helpers/notes_helper.rb

@@ -148,14 +148,14 @@ def subscribe_button(ontology_id)
         ont = LinkedData::Client::Models::Ontology.find_by_acronym(ontology_id).first
       end
       subscribed = subscribed_to_ontology?(ont.acronym, user)  # application_helper
-      sub_text = subscribed ? "Unsubscribe" : "Subscribe"
+      sub_text = subscribed ? "Unsubscribe from" : "Subscribe to"
       params = "data-bp_ontology_id='#{ont.acronym}' data-bp_is_subbed='#{subscribed}' data-bp_user_id='#{user.id}'"
     rescue
       # pass, fallback init done above begin block to scope parameters beyond the begin/rescue block
     end
     spinner = '<span class="notes_subscribe_spinner" style="display: none;">' + image_tag("spinners/spinner_000000_16px.gif", style: "vertical-align: text-bottom;") + '</span>'
     error = "<span style='color: red;' class='notes_sub_error'></span>"
-    return "<a href='javascript:void(0);' class='subscribe_to_notes link_button' #{params}>#{sub_text} to notes emails</a> #{spinner} #{error}".html_safe
+    return "<a href='javascript:void(0);' class='subscribe_to_notes link_button' #{params}>#{sub_text} notes emails</a> #{spinner} #{error}".html_safe
   end
 
   def delete_button