Chrome extension - pass function result from content script to popup.js - google-chrome

Question

I have extension with popup.html which has popup.js in it.
I use popup.js to call function located in content script using chrome.tabs.sendMessage -method.
This is working nicely, but..
How do I return the value of the function back to popup.js ? Do I need to set up a listener on the popup.js aswell or what ?
On my popup.js I have:
chrome.tabs.sendMessage(tab.id, {
expiryRequest: 'expiry '
}, function (response) {
if (response.refreshResponse === true) {
console.log('Expiry taken');
} else {
console.log('Expiry NOT taken');
}
});
This part works great..
On my content script I read certain div into a vartiable "result".
At the end of the function on content script I have used.
return result;
or
return true;
None of those returns anything back tuo popup.js.
What do I need to change in order to get my return to work from content script to popup.js ?

Answer 1

You should not return your result, but send it back.
chrome.runtime.onMessage callbacks take 3 parameters: the message, the sender information, and the sendResponse callback.
To pass a response back, sendResponse must be called:
chrome.runtime.onMessage.addListener(function(message, sender, sendResponse){
if(message.ping) sendResponse({pong: true});
});
However, there's an additional trick to it. The event listener should either reply immediately (i.e. synchronously, before it exits) or signal that it will reply later. This is done with the return value:
chrome.runtime.onMessage.addListener(function(message, sender, sendResponse){
if(message.ping) {
chrome.storage.local.get("shouldReply", function(result){
// This is asynchronous: by now the listener returned
if(result.shouldReply) sendResponse({pong: true});
});
}
return true; // Indicate that you will eventually call sendResponse
});
Unless you do this, sendResponse reference is invalidated when the listener exits and an undefined response is sent.
One more caveat: you should call sendResponse no more than once; it will generate an error otherwise.