title: How to check whether a string is among the `options` of a `select` in jquery?
body: <p>The html codes are like this:</p>
  
  <pre><code>&lt;select id="select1"&gt;
    &lt;option value="volvo"&gt;Volvo&lt;/option&gt;
    &lt;option value="saab"&gt;Saab&lt;/option&gt;
    &lt;option value="mercedes"&gt;Mercedes&lt;/option&gt;
    &lt;option value="audi"&gt;Audi&lt;/option&gt;
  &lt;/select&gt; 
  </code></pre>
  
  <p>I was wondering how to write a function to test whether a <code>string</code> is among the <code>option</code> of a select, such as</p>
  
  <pre><code>test_in("volvo", "select1")      // Return True
  test_in("asdf", "select1")      // Return False
  test_in("AUDI", "select1")      // Return False
  </code></pre>
  
  <p>Does anyone have ideas about this? Thanks!</p>