Javascript (NodeJS): How to get data back from a Google Calendar API callback

Question

Regarding this example: https://developers.google.com/google-apps/calendar/quickstart/nodejs

I want to change the listEvents to return a JSON array of the events.

It's currently called like this:

authorize(JSON.parse(content), listEvents);

where "listEvents" is the function passed to the callback:

function authorize(credentials, callback) {

I tried add a return statement to ListEvents and then this:

var jsonEvents = authorize(JSON.parse(content), listEvents);
console.log("Json Events="); 
console.log(jsonEvents);

I know it's going async on me, because I get the above console.logs before the console.log output of the listEvents function. I also tried throwing in the "await" word, but no luck.

and I tried setting an extra parameter in in listEvents:

var jsonEvents; 
authorize(JSON.parse(content), listEvents(jsonEvents));
console.log("Json Events="); 
console.log(jsonEvents);

which resulted in "typeError: callback is not a function".

Update: based on @Tuches answer, I got this to work. Would like to know if it was necessary to expand this far.

  authorize(JSON.parse(content), function(token) {
      console.log("Got Token"); 
      //console.log(token);
      listEvents(token, function(jsonResult) {
          console.log("Json Callback Events="); 
          console.log(jsonResult); 
      }); 
    });

Tutch · Accepted Answer · 2017-12-01 18:34:36Z

1

I don't know about the google calendar API, but giving it a quick read the second argument is a callback function. This means that the result of authorize will end and then listEvents will be called. So actually what you should do is either handler this data return inside listEvents or you can modify listEvents to return a callback, like:

function listEvents(auth, callback) {
    // ... implementation of the function
    // When the function is done an there's data to
    // return, callback the data
    callback(data);
}

This way you will can handle returning data from listEvents by doing something like this:

authorize(JSON.parse(content), listEvents(data, function(response) {
        console.log(response); // <-- return from listEvents    
    })
);

EDIT: small correction on the code.

edited Dec 1, 2017 at 18:34

answered Dec 1, 2017 at 18:16

Tutch

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4 Comments

NealWalters Over a year ago

Okay, that makes sense, But I get this error in one of the API libraries: λ node testGoogleCalendarAPI.js E:\GitHub\NealWalters\RabbiJoseph\node_modules\googleapis\lib\apirequest.js:150 req = authClient.request(options, callback); ^ TypeError: authClient.request is not a function

NealWalters Over a year ago

I was able to get the token back from authorize, then call listEvents in a sync fashion, but listEvents is further complicated because it has a call back from calendar.list.events: function(err, response).

NealWalters Over a year ago

See my update, got it working, but maybe not the best way.

Sudeep Acharya Over a year ago

This gives the following error: ReferenceError: data is not defined

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