title: Finding array element's position whitin the element itself in Javascript
body: <p>Цhat is the most effective way to find an element position within an array, if we got access to the element itself?</p>
  
  <pre><code>var arr = [];
  for (var i = 0; i &lt; 10; i++) {
      arr[i] = {test: Math.floor(Math.random() * 101)}
  }
  var test = arr[Math.floor(Math.random() * 11)];
  </code></pre>
  
  <p>Now how can I get the position of the element that <code>test</code> refer to?</p>