title: What does empty array.slice(0).push(anything) mean?
body: <p>I want to clone a new array from an existing one and push in an element.
  Unfortunately, the existing array is an empty one, so it's like:</p>
  
  <pre><code>[].slice().push(65)
  </code></pre>
  
  <p>the output of above expression is 1.</p>
  
  <p>Why is it 1?</p>