title: Passing value from one field to another
body: <p>I want to pass the value <code>9112232453</code> of one textfield to another.</p>
  
  <p>I know I need Javascript for this but I don't know how to do it.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;form method = "post" action=""&gt;
    &lt;input type="checkbox" name="phone" value="9112232453" onclick='some_func();' &gt;
    &lt;input type="text" name="phone" value="" id="phone"&gt;
    &lt;input type="submit" name="Go"&gt;
  &lt;/form&gt; 
  </code></pre>
  
  <p>Then later, I want to use the value in my php.</p>