node.js asynchronous passing variable between functions

Question

i am taking my first steps with node.js and i came across this issue with passing variable in asynchronous way. I have this piece of code im using to create Facebook user:

req.tmpPassport = {};
var fb = new fbgraph.Facebook(accessToken, 'v2.2');
function initUser() {
    fb.me(function (err, me) {
        req.tmpPassport.me = me;
        console.log(req.tmpPassport.me) // works
    });
}

console.log(req.tmpPassport.me) // not working -> undefined var

i tried to figure out why the second log isn't working and i ended up reading about synchronous and asynchronous functions, so in attempt to implement what i read i tried coming up with a solution using callbacks, but no success. my last attempt was this:

req.tmpPassport = {};
var fb = new fbgraph.Facebook(accessToken, 'v2.2');
function initUser() {
    fb.me(function (err, me) {
        req.tmpPassport.me = me;
    });
    fb.my.events(function (err, events) {
        //console.log(events);
        req.tmpPassport.events = events;

    });
    fb.my.friends(function (err, result) {
        req.tmpPassport.results = result;
    });
}
function passUser(){
    console.log(req.tmpPassport);
    return req.tmpPassport;
}
cp.exec(initUser, passUser);

but its not working... what i am actually trying to achieve its to render this object with my express router var which looks like this:

   router.get('/welcome', securePages, function(req, res, next){
        res.render('welcome', {title:'Welcome to aDating', user:req.tmpPassport});
    })

but i cant figure out how to pass this object only after created...any help please?

filype · Accepted Answer · 2015-08-20 08:47:59Z

3

A method of chaining function calls when certain async tasks are done is one way to deal with this.

Looking at the first snippet of code, it would be rewritten as follows:

req.tmpPassport = {};
var fb = new fbgraph.Facebook(accessToken, 'v2.2');
function initUser() {
    fb.me(function (err, me) {
        console.log(req.tmpPassport.me) // works
        req.tmpPassport.me = me;

        // triggers execution of the next step
        post_populating_passport();
    });
}

function post_populating_passport() {
    // this function is only executed after the callback from the async call
    console.log(req.tmpPassport.me);
}

edited Aug 20, 2015 at 8:47

answered Jul 18, 2015 at 0:28

filype

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webdevfe · Accepted Answer · 2015-07-18 00:47:02Z

0

Node.js is an asynchronous programming language, a fundamental concept in its core. You either need to use function callbacks (not a good practice) or available npms utilities for async flow.

answered Jul 18, 2015 at 0:47

webdevfe

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