OpenSocialHelloWorld.html

<h1>OpenSocial Hello World</h1>

<script type="text/javascript">

var viewer = null;

/**
 * Initial data request to load viewer
 */
function getViewerData() {
  var req = opensocial.newDataRequest();
  req.add(req.newFetchPersonRequest(
    opensocial.IdSpec.PersonId.VIEWER), "viewer");

  req.send(getDataCallback);
}

/**
 * Callback handler to process the response
 * @param {Object} data
 */
function getDataCallback(data) {
  if (data.hadError()) {
    var err = "Processing Error: " + data.get("viewer").getErrorMessage();
    writeMessage(err + "<br />You should install the app");
    return;
  }
  viewer = data.get("viewer").getData();
  if(viewer) {
    writeMessage("Hello, " + viewer.getDisplayName());
  } else {
    writeMessage("Wow, you don't exist.");
  }
}

/**
 * Conveinence method to write our message to the page
 * @param {Object} msg
 */
function writeMessage(msg) {
  var elem = document.getElementById("message");
  elem.innerHTML = msg;
}

// Register to look for initial data
gadgets.util.registerOnLoadHandler(getViewerData);
</script>

<!-- Here's the div where our Hello World message goes -->
<div id="message"></div>