title: Fill textarea value from url parmeter then write value to iframe
body: <p>i have textarea &amp; iframe with <code>src='about:blank'</code> , the textarea will be filld with alittle HTML [1 or 2 tags to preview] that obtained from url parameter "preview" for example [before decoding url]</p>
  
  <pre><code>http://example.com/?preview=&lt;h1&gt;this-is-heading-line&lt;/h1&gt;&lt;p&gt;and-this-is-paragraph&lt;/p&gt;
  </code></pre>
  
  <p><strong>Then</strong> [in the same order] write textarea's value to iframe using</p>
  
  <pre><code>var textarea_value = document.getElementById('mytextarea').value  
  document.getElementById('preview').contentDocument.write(textarea_value);
  </code></pre>
  
  <p>when the page is fully loaded using javascript .. how to do that in the same order ? what can i use <code>window.onload</code> or <code>$(document).ready</code> or <code>$(window).ready</code> ?</p>