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              <html>
  <body>
    <center><h1>Widget Maker</h1></center>
    <div id="widget-holder">
      <p><label>Widget</label></p>
      <div id="widget"></div>
    </div>
    <div id="code">
      <p><label>Widget code</label></p>
      <p><textarea id="codebox" cols="40" rows="10">$().html("<h1>Hello Widget World!</h1>");
setTimeout(function() {
  $("h1").text("Goodbye Widget World!");
}, 3000);</textarea></p>
      <p><button type="submit" id="run-button">Run Widget</button></p>
    </div>
  </body>
</html>
            
          
!
            
              body {
  font-family: Helvetica, Verdana, Arial, sans-serif;
  font-size: 14px;
  background-color: #7FDBFF;
  color: #001F3F;
  max-width: 720px;
}

h1, label, button {
  text-transform: uppercase;
}

label {
  color: #001F3F;
  font-weight: bold;
}

button {
  background-color: #001F3F;
  color: white;
  border: none;
  padding: 20px;
  cursor: pointer;
}

#code {
  margin-right: 380px;
}

#codebox {
  font-size: 14px;
  border: none;
  margin: 0px;
  padding: 8px;
  font-family: monospace;
}

#widget-holder {
  float: right;
  width: 350px;
  height: 150px;
  margin-top: -14px;
}

#widget {
  padding: 8px;
  background-color: white;
  width: 100%;
  height: 100%;
}
            
          
!
            
              /* Used as the worker prelude - runs in the worker context */
function setupWorker(widgetFunc) {
    
  var postMessage = self.postMessage;
    
  /* Constructs a view manipulation object */
  function view(id) {
    function updateView(action, content) {
      postMessage.call(self, {
        id: id,
        action: action,
        content: content
      }); 
    }
    
    return {
      html: function(val) {
        updateView("html", val);
      },
      text: function(val) {
        updateView("text", val);
      }
    };
  }
  
  self.$ = view;
  
  // remove widget code access to postMessage
  self.postMessage = null;
  
  // freeze context so widget code can't change it
  Object.freeze(self);
  
  // run the widget's code
  widgetFunc();
}

/* ----------------------------------------------------- */

/*
 * Create the code to run in the web worker.
 * Use the contents of the setupWorker function concatenated
 * with the widget code wrapped in a function.
 */
function createCode() {
  var widgetCode = $("#codebox").val();
  var code = setupWorker.toString() +
      "\nfunction widgetCode() {" + widgetCode + "}" +
      "\nsetupWorker(widgetCode);";
  return code;
}

/*
 * Handle messages from the worker relating to updating the
 * widget's view content.
 */
function handleMessage(msg) {
  var data = msg.data;
  var content = html_sanitize(data.content);
  var sel = "#widget";
  if(data.id != null) sel += " " + data.id;
  
  if(data.action == 'html') {
    $(sel).html(content);  
  } else if(data.action == 'text') {
    $(sel).text(content);
  } else {
    content.warn("Unrecognized action: %s", data.action);
  }
}

function runWorker() {  
  console.clear();
  var code = createCode();
    
  // Needs support for Blob (IE10+)
  var blob = new Blob([code], { type: 'application/javascript' });

  var worker = new Worker(URL.createObjectURL(blob));
  worker.onmessage = handleMessage;
}

$(document).ready(function() {
  console.clear();
  $("#run-button").click(runWorker);
});
            
          
!
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