title: Why spread operator turn my array into numbers
body: <p>i have </p>
  
  <p><code>a = [[1,2,3],[4,5,6]]</code></p>
  
  <p>How come when i write</p>
  
  <p><code>console.log(...a.shift())</code>
  it gives me <code>1 2 3</code>
  but not <code>1,2,3</code> nor <code>[1, 2, 3]</code>
  can anyone explain me the mechanism behind this?</p>