title: adding <path> to iframe run time
body: <p>I Have an iframe chart from some website and all I wanna do is to add a horizontal line throw the chart. I add some JS but it does not take effects. I wonder if someone can help me with that.
  this is the code:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;&lt;/title&gt;
  
      &lt;script
    src="https://code.jquery.com/jquery-3.3.1.min.js"
    integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8="
    crossorigin="anonymous"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;iframe id="frame" width="450" height="260" style="border: 1px solid #cccccc;" src="https://thingspeak.com/channels/507016/charts/1?bgcolor=%23ffffff&amp;color=%23d62020&amp;dynamic=true&amp;results=60&amp;title=Height+Level+River+%28Murazzi+Po%29&amp;type=line&amp;xaxis=Time+&amp;yaxis=Measured+Height+%28+m+%29"&gt;&lt;/iframe&gt;
  &lt;/body&gt;
  
  
  &lt;/html&gt;
  </code></pre>
  
  <p>and this is the JS that help me to inject</p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      var $iframe = $('#frame');
  
  $iframe.ready(function() {
  
      setTimeout( function(){ 
  
      $iframe.contents().find(".highcharts-series-group").append('&lt;path fill="none" d="M 62 132.5 L 415 132.5" stroke="#010" stroke-width="1" zIndex="1" opacity="1"&gt;&lt;/path&gt;');
  
    }  , 3000 );
  
  
  
  &lt;/script&gt;
  </code></pre>
  
  <p>I wait 3 seconds to ensure that iframe loads completely.</p>
  
  <p>any help will be appreciated.</p>