title: How to execute a callback after `window.open`?
body: <p>I try to execute a callback after I opened a new window from JavaScript:</p>
  
  <pre><code>newwindow = window.open(myurl,'mywindow',false);
  
  newwindow.onload = function() {
    console.log("callback");
    newwindow.console.log("callback");
  }
  </code></pre>
  
  <p>However, the defined callback is neither executed in the parent, nor in the child window. What am I doing wrong?</p>