title: Monitoring a value change on an input element
body: <pre><code>US Price: &lt;input type="text" name="us_price" id="us_price" value="1000" onchange="$('#uk_price').val($(this).val()*2);" /&gt;
  UK Price :&lt;input type="text" name="uk_price" id="uk_price" value="2000" /&gt;
  </code></pre>
  
  <p>Here if a user enters a value in US price it will double and set in UK Price. What I want is to write a separate function to monitor the value change in UK price input field. Please help.</p>
  
  <p>for example: if value changed show <code>alert("Done!")</code>.</p>