title: Push an empty element into javascript array
body: <p>How can I push empty element to an existing Js array, lets assume :</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var arr = [54,77,21];
  var target = [54,77,21,,,,36];
  arr.push(); //do not append an empty element into the array.
  arr.push();
  
  console.log(JSON.stringify(arr)); //output: [54,77,21]</code></pre>
  </div>
  </div>
  </p>
  
  <p>How to append empty elements so "arr" will be equivalent to "target" array? </p>