title: Array.map 1 element to multiple element
body: <p>I have <code>[3, 16, 120]</code>. when I do <code>[3, 16, 120].map(mapper)</code>, I want to achieve, for example <code>[4,5,  17,18,  121,122]</code> i.e. each element map to n+1 and n+2. This is of course an example - what I want is to simply push multiple values from mapper function</p>
  
  <p>Do I have to use Array.each and push to an array, or is it possible to do it with Array.map (or other built-in api)</p>