title: What does => do and what is it called in the context below?
body: <p>What does (a=>) do in the context below?</p>
  
  <pre><code>function findOutlier(int){
    var even = int.filter(a=&gt;a%2==0);
    var odd = int.filter(a=&gt;a%2!==0);
    return even.length==1? even[0] : odd[0];
  }
  </code></pre>