title: In Javascript a dictionary comprehension, or an Object `map`
body: <p>I need to generate a couple of objects from lists in Javascript. In Python, I'd write this:</p>
  
  <pre><code>{key_maker(x): val_maker(x) for x in a_list}
  </code></pre>
  
  <p>Another way to ask is does there exist something like <code>jQuery.map()</code> which aggregates objects? Here's my guess (doesn't work):</p>
  
  <pre><code>var result = {}
  $.map(a_list, function(x) {
      $.extend(result, {key_maker(x): val_maker(x)})
  })
  </code></pre>