title: JavaScript - Check multiple SELECT for duplicate options
body: <p>This question is based on <a href="https://stackoverflow.com/questions/19160330/javascript-multiple-select-boxes-remove-selected-options">THIS QUESTION</a></p>
  
  <p>When an option from one of the SELECT boxes were selected, I wanted the rest to be repopulated, without said option, but instead, is there an easy way to loop through all these select items, to ensure the same option hasn't been selected twice?</p>
  
  <p>Thanks.</p>
  
  <pre><code>Person Number 1
  &lt;select name="person1"&gt;
  &lt;option value="null"&gt;Please Select an option&lt;/option&gt;
  &lt;option value="1"&gt;1&lt;/option&gt;
  &lt;option value="2"&gt;2&lt;/option&gt;
  &lt;option value="3"&gt;3&lt;/option&gt;
  &lt;/select&gt;
  
  Person Number 2
  &lt;select name="person2"&gt;
  &lt;option value="null"&gt;Please Select an option&lt;/option&gt;
  &lt;option value="1"&gt;1&lt;/option&gt;
  &lt;option value="2"&gt;2&lt;/option&gt;
  &lt;option value="3"&gt;3&lt;/option&gt;
  &lt;/select&gt;
  
  Person Number 3
  &lt;select name="person3"&gt;
  &lt;option value="null"&gt;Please Select an option&lt;/option&gt;
  &lt;option value="1"&gt;1&lt;/option&gt;
  &lt;option value="2"&gt;2&lt;/option&gt;
  &lt;option value="3"&gt;3&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>Basic Overview:
  JavaScript loop to ensure none of the options have been selected twice?</p>