title: Waiting for child window loading to complete
body: <p>Is there an easy hook for detecting that a window opened by a script has finished loading? Basically, I want the equivalent of the <code>onLoad()</code> hook, but I can't set it directly -- assume that the child document is a given and I can't actually put any code of my own in it.</p>
  
  <p>For instance, say I have the following two files:</p>
  
  <p><code>parent.html</code>:</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;
      &lt;title&gt;Parent&lt;/title&gt;
    &lt;/head&gt;
    &lt;script type="text/javascript"&gt;
      var w;
      function loadChild() {
        w = window.open();
        w.location.href="child.html";
        // block until child has finished loading... how?
        w.doSomething();
      } 
    &lt;/script&gt;
  &lt;/html&gt;
  &lt;body&gt;
    I am a parent window. &lt;a href="javascript:loadChild()"&gt;Click me&lt;/a&gt;.
  &lt;/body&gt;
  </code></pre>
  
  <p><code>child.html</code>:</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;
      &lt;title&gt;Child&lt;/title&gt;
    &lt;/head&gt;
    &lt;script type="text/javascript"&gt;
      function doSomething() {
        alert("Hi there");
      }
    &lt;/script&gt;
  &lt;/html&gt;
  &lt;body&gt;
    I am a child window
  &lt;/body&gt;
  </code></pre>
  
  <p>Since setting location.href is non-blocking, <code>w.doSomething()</code> isn't defined yet and the <code>doSomething()</code> call blows up. How can I detect that the child has finished loading?</p>