title: Backbone collection: add logic to item models
body: <p>I update a Backbone collection from array of bare objects by using <code>reset</code>:</p>
  
  <pre><code>const collection = new Backbone.Collection();
  // ... 
  const switches = [
      { color: "red", on: false },
      { color: "green", on: false },
      { color: "blue", on: true }
  ];
  collection.reset(switches);
  </code></pre>
  
  <p>Now there are 3 models in my collection. I want them to have <code>toggle()</code> method: </p>
  
  <pre><code>toggle: function() { 
      this.save({ on: !this.get("on") }) 
  }
  </code></pre>
  
  <p>How can I add it?</p>