title: new Array(n) creates empty arrays; [...new Array(n)] creates undefined arrays. Why?
body: <p>new Array(n) generates an array of empty numbers. e.g. <code>new Array(5)</code> generates <code>[empty × 5]</code></p>
  
  <p><code>[...new Array(n)]</code> generates an array of undefined numbers. e.g. <code>[...new Array(5)]</code> generates <code>[undefined, undefined, undefined, undefined, undefined]</code></p>
  
  <p>Which part of the process converts empty values in undefined values?</p>