javascript - Chrome Extension sendResponse callback value not being sent -

i'm coding chrome extension interacts gmail api (chrome 45 version) , having issues sending message background.js content-script. async aspect issue lies. how can message sent after callback?

//---------in content script--------- chrome.runtime.sendmessage({ messageid: _id }, function (response) {         console.log('the respose.messagepayload is: ' + response.messagepayload);  });  //---------in background script--------- chrome.runtime.onmessage.addlistener(function (request, sender, sendresponse) {     getmessage('me', request.messageid, function (payload) {         //i want send response here         //this executes , grabs payload of data api, isn't sending message content-script         sendresponse({ messagepayload: payload });      });     //this synchronous call sends message content-script     //sendresponse({ messagepayload: "payload" });     return true; });  function getmessage(userid, messageid,callback) {     var request = gapi.client.gmail.users.messages.get({         'userid': userid,         'id': messageid     });     request.execute(callback); } 

chrome extension message passing: response not sent

you should sending sendresponse function in callback.

getmessage('me', request.messageid, sendresponse); 

then execute when getmessage call completes.

function getmessage(userid, messageid, sendresponse) {     var request = gapi.client.gmail.users.messages.get({         'userid': userid,         'id': messageid     });      request.execute(function(response) {         sendresponse({messagepayload: response.payload});     }); } 

another possible solution:

1. get tab id sender object.
2. instead of callback function send tab id getmessage function.
3. now, callback function within getmessage function send payload content script.
4. add similar onmessage listener in content script receive payload , want payload.

your code like:

//---------in background script--------- chrome.runtime.onmessage.addlistener(function (request, sender,sendresponse) {     getmessage('me', request.messageid, sender.tab.id); });  function getmessage(userid, messageid, tabid) {     var request = gapi.client.gmail.users.messages.get({         'userid': userid,         'id': messageid     });     request.execute(function(response) {         // whatever response want sent         // below url explains response object         // https://developers.google.com/gmail/api/v1/reference/users/messages#resource         // assuming want send payload         chrome.tabs.sendmessage(tab.id, {messagepayload: response.payload});     }); }  //---------in content script--------- chrome.runtime.sendmessage({ messageid: _id });  chrome.runtime.onmessage.addlistener(function (request, sender,sendresponse) {     // verify request getmessage callback     // because listen request extension     if (request.messagepayload) {         console.log('the respose.messagepayload is: ' + request.messagepayload);     } }); 

i hope helps.