title: elasticsearch node client using mget on index alias bringing back docs not in alias
body: <p>I am using the node js client for ES.</p>
  
  <p>I am doing an mget but using alias for index field and not an actual index. 
  It works in the sense it brings back results but one of the documents is not in the alias but in the underlying index i.e. it should fail the alias test and so not come come back in the result but it is.</p>
  
  <pre><code>itemIds = ['3504479-4-41','3504700-4-41'];//test, second id is not in alias
  esClient.mget({
       index: 'live_articles',
       _source: ['id','itemTypeId','headline','itemUrl','startDate','summary', 'onlineStatus'],
              body: {ids: itemIds}
          }, function (err, resp) {
              var items = [];
              console.log(resp.docs);
          });
  </code></pre>
  
  <p>does mget in this usage instance ignore the conditions of the alias and just use the alias to get the index?</p>