title: How do I change a JavaScript array in place?
body: <p>How do I change a JS array in place (like a Ruby "dangerous" method, e.g., "!")</p>
  
  <p><strong>Example:</strong></p>
  
  <p>If I have this:</p>
  
  <p>var arr = [1, 2, 3]</p>
  
  <p>How can I make this:</p>
  
  <p>arr === [2, 4, 6]</p>
  
  <p>(assuming I have an appropriate function for doubling numbers) in one step, without making any more variables?</p>