title: Why does [5,6,8,7][1,2] = 8 in JavaScript?
body: <p>I can't wrap my mind around this quirk.</p>
  
  <pre><code>[1,2,3,4,5,6][1,2,3]; // 4
  [1,2,3,4,5,6][1,2]; // 3
  </code></pre>
  
  <p>I know <code>[1,2,3] + [1,2] = "1,2,31,2"</code>, but I can't find what type or operation is being performed.</p>