title: Performance difference between []+[] and [].join(',')+[].join(',')
body: <p>Just while fiddling through arrays i found this.</p>
  
  <p>why there is significant difference between the following three statements:</p>
  
  <pre><code>[1,2]+[3,4];
  
  [1,2].toString()+[3,4].toString();
  
  [1,2].join(',')+[3,4].join(',');
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/mitQX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mitQX.png" alt="enter image description here"></a>
  And if <code>[1,2]+[1,2]</code> performs the same as converting to string and then joining the two strings, then shouldnt be performance of them be somewhat similar</p>
  
  <p>This question is inspired from this <a href="https://stackoverflow.com/a/7130218/3556874">answer</a></p>