title: Is there a data structure like the Java Set in JavaScript?
body: <p>I want to use a data structure in JavaScript that can be used to store number of IDs. I should be able to check if a key already exists in that set, something like Java Sets.</p>
  
  <p>I want to achive same behaviours as follows (this code is in Java):</p>
  
  <pre><code>Set&lt;String&gt; st = new HashSet&lt;String&gt;();
  //add elemets
  
  if(st.contains("aks") ){
    //do something
  }
  </code></pre>
  
  <p>I want a JavaScript/dojo equivalent of the above code.</p>