Chrome Extension Development : Message passing Problem

Question

Hi All, Having a problem while passing messages using content scripts in Google chrome extension dev My Code structure looks like this:

popup.html:

var oList;
function getHTML()
{
    chrome.tabs.getSelected(null, function(tab) {
     chrome.tabs.sendRequest(tab.id, {action:"getHTML"}, function handler(response) {
      oList = response.dom;
     });
   });

   alert("oList = "+oList );
}

and my content Script looks like this:

chrome.extension.onRequest.addListener(
  function(request, sender, sendResponse) {
  if(request.action == "getHTML"){
   sendResponse({dom: document.getElementsByTagName("HTML").length});   
     }
  });

When I debug my code by putting a breakpoint at "oList = response.dom;" in my popup.html, i get the right value set from the content script. But while executing the extension, the "alert("oList = "+oList );" code from the popup.html seems to be executing first before it goes to the server.. And therefore, its value is not being set.. Can somebody tell me if I am wrong somewhere ?

Answer 1

Most Chrome API methods are asynchronous. It means that when you are calling them the script doesn't wait for their response and simply continues executing. If you want to execute something on response you should put it inside callback function:

chrome.tabs.getSelected(null, function(tab) {
 chrome.tabs.sendRequest(tab.id, {action:"getHTML"}, function handler(response) {
  oList = response.dom;
  alert("oList = "+oList );
 });
});