title: concat array after filter javascript
body: <p>this code doesn't work</p>
  
  <pre><code> var arr1 = ["a", "b", "c"];
   var arrayJoin=[];
  arrayJoin.concat(arr1.filter(function (val) {
                      return val == "a";
      }));
  
  console.log(arrayJoin);
  </code></pre>
  
  <p>this works fine </p>
  
  <pre><code>arrayJoin=arr1.filter(function (val) {
                      return val == "a";
      }));
  </code></pre>
  
  <p>any idea how to concat the filter array?</p>