How to make the following template helper reactive (Meteor)?

I have Chapters collection, and I show a list of chapters in one of the templates:

<template name="chapterItem">
  <div class="chapter clearfix {{isCurrentChapter}}">
    <div class="chapter-arrows">
      <a class="move-up" href="javascript:;"><i class="ion-arrow-up-a"></i></a>
      <a class="move-down" href="javascript:;"><i class="ion-arrow-down-a"></i></a>
    </div>
    <h4><a class="open-chapter" href="javascript:;">{{title}}</a></h4>
    <a class="delete-current-chapter" href="javascript:;"><i class="ion-close-circled"></i></a>
  </div>
</template>

As you can see, I created a isCurrentChapter to use like this:

// book_page.js
Template.bookPage.events
  "click .open-chapter": function() {
    localStorage.setItem "currentChapter", this._id
  }

// chapter_item.js
Template.chapterItem.helpers({
  isCurrentChapter: function() {
    var currentChapterId = localStorage.getItem("currentChapter");
    var selectedChapterId = this._id;
    if selectedChapterId === currentChapterId) {
      return "active";
    }
  }
});

The problem now is that the active is returned only changes when the page loads.

How can I do it so that isCurrentChapter becomes reactive? Fires up on the click .open-chapter event?