background.html

<script>
 
    // Array to hold callback functions
    var callbacks = []; 
	
    // This function is called onload in the popup code
    function getPageInfo(callback) 
    { 
        // Add the callback to the queue
        callbacks.push(callback); 

        // Injects the content script into the current page 
        chrome.tabs.executeScript(null, { file: "js/content_script.js" }); 
    }; 

    // Perform the callback when a request is received from the content script
    chrome.extension.onRequest.addListener(function(request) 
    { 
        // Get the first callback in the callbacks array
        // and remove it from the array
        var callback = callbacks.shift();

        // Call the callback function
        callback(request); 
    }); 

</script>
<script>
chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab){
  if(changeInfo.status == "loading"){
    //chrome.tabs.executeScript(tabId, { file: "js/pageLoaded.js" });  
    var q;
	var tabURL = tab.url;

	q = queryValue(tabURL, 'q');
	if(q!=null) {
		chrome.browserAction.setBadgeText({'text': '+'});
	} else {
	//Look at domain name and see if we can recognize it
	var domain;
	var re1='.*?';	// Non-greedy match on filler
	var re2='((?:[a-z][a-z\\.\\d\\-]+)\\.(?:[a-z][a-z\\-]+))(?![\\w\\.])';	// Fully Qualified Domain Name 1

	var p = new RegExp(re1+re2,["i"]);
	var m = p.exec(tabURL);
	if (m != null)
	  {
	   domain=m[1];
	  }
	if(domain=='www.ncbi.nlm.nih.gov') {
		if(queryValue(tabURL, 'term')!=null) {
			chrome.browserAction.setBadgeText({'text': '+'});
		}
	}
	else {
		chrome.browserAction.setBadgeText({'text': ''});
	}
}

function queryValue(url, name) {

  name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
  var results = regex.exec(url);
  if( results == null )
    return;
  else
    return decodeURIComponent(results[1].replace(/\+/g, " "));

}
    
  }
});
</script>