<script type="text/javascript">
    window.name = 'I was there!';  // 这里是要传输的数据，大小一般为2M，IE和firefox下可以大至32M左右
                     // 数据格式可以自定义，如json、字符串
  </script>

<script type="text/javascript">
    var state = 0, 
    iframe = document.createElement('iframe'),
    loadfn = function() {
      if (state === 1) {
        var data = iframe.contentWindow.name;  // 读取数据
        alert(data);  //弹出'I was there!'
      } else if (state === 0) {
        state = 1;
        iframe.contentWindow.location = "http://a.com/proxy.html";  // 设置的代理文件
      } 
    };
    iframe.src = 'http://b.com/data.html';
    if (iframe.attachEvent) {
      iframe.attachEvent('onload', loadfn);
    } else {
      iframe.onload = loadfn;
    }
    document.body.appendChild(iframe);
  </script>

<script type="text/javascript">
    iframe.contentWindow.document.write('');
    iframe.contentWindow.close();
    document.body.removeChild(iframe);
  </script>