title: jQuery map does not work with json array
body: <p>I have a $.post jQuery call that calls a php file. The file then returns a JSON encoded array. Then, the array is mapped to edit some of the data in the array. However, I get the error <code>arr.map is not function</code>.</p>
  
  <p>Here is the array being passed in the $.post call.</p>
  
  <pre><code>[{"set":"Alpha","key":"256"},
  {"set":"Omega","key":"671"},
  {"set":"Theta","key":"762"},
  {"set":"Beta","key":"462"}]
  </code></pre>
  
  <p>Here is the map function.</p>
  
  <pre><code>idHash = {'Alpha': '1', 'Beta': '2', 'Theta': '3', 'Omega': '4'};
  var arr = arr.map(function(item){
      item.set = idHash[item.set]
      return item;
  })
  </code></pre>
  
  <p>After the map function, the array should look like this.</p>
  
  <pre><code>[{"set":"1","key":"256"},
  {"set":"4","key":"671"},
  {"set":"3","key":"762"},
  {"set":"2","key":"462"}]
  </code></pre>