nodejs http request returns `undefined` - node.js

Question

While trying to debug the following get request, I notice that it returns undefined and then runs the code for the response.
configs is a json object with all the parameters defined. I am also, for some reason, getting a response form the php server saying that grant-type is invalid or can't be found, although when debugging it is passing the correct parameter from the configs file.
How can I correct my code?
var http = require("http");
var querystring = require("querystring");
var _ = require("underscore");
apiCaller = {};
apiCaller.token = null;
var server=http.createServer(function(req,res){});
server.listen(8080);
apiCaller._get = function (context, config, fn) {
// request to obtain our oauth token
var options = {
method: "GET",
hostname: config.host,
client_id: config.clientId,
client_secret: config.clientSecret,
grant_type: config.grant_type,
path: "/my/path/to/token",
headers : {
'Content-Type': "application/json",
'Accept': "application/json"
}
};
var callback = function(response) {
console.log('STATUS: ' + response.statusCode);
console.log('HEADERS: ' + JSON.stringify(response.headers));
var str = '';
//another chunk of data has been recieved, so append it to `str`
response.on('data', function (chunk) {
str += chunk;
});
// error response
response.on("error", function (error) {
if ( !context ) {
console.error("Something went wrong with the api response.");
return;
}
context.done(new Error("Something went wrong with the api response."));
});
//the whole response has been recieved, so we just print it out here
response.on('end', function () {
apiCaller.token = JSON.parse(str).access_token;
// we want to stop the request if token is not correct
if ( !apiCaller.token || apiCaller.token === undefined || apiCaller.token === null ) {
if ( !context ) {
console.error("Something went wrong with the token. Wrong token! Token: %s", apiCaller.token);
return;
}
console.error("Token: %s", apiCaller.token);
context.done(new Error("Something went wrong with the token. Wrong token!"));
}
});
};
var request = http.request(options, callback);
request.on('error', function(e) {
console.log('problem with request:');
});
request.end();
};

Answer 1

It is an asynchronous function. Asynchronous functions (which are kind of the bread-and-butter of Node.js) typically return nothing. Instead, what you might think of as the return value is passed to the callback function. That's what's happening here.

Answer 2

As Trott says, It's asynchronous, it's possible that request.end() is executing before callback function has finished....