text: window.getVersion = function() { 
    if (!chrome.extension.version_) { 
      var xhr = new XMLHttpRequest(); 
      xhr.open('GET', chrome.extension.getURL('manifest.json'), false); 
      xhr.onreadystatechange = function() { 
        if (this.readyState == 4) { 
          var manifest = JSON.parse(this.responseText); 
          chrome.extension.version_ = manifest.version; 
        } 
     }; 
     xhr.send(); 
   } 
   return chrome.extension.version_; 
  }