Update the variable value after asynchronous http call - node.js

Question

I have a firebase function called getRequest which contains simple http calls using request npm package and a variable named result which will should contain the body response from the http call after request completed.
However, the request output is a "this should be replaced" string, because the http call runs asynchronously.
How do you get the result variable to contain the body response from the http call?
const functions = require('firebase-functions');
const request = require('request');
exports.getRequest = functions.https.onRequest(() => {
let result = "this should be replaced";
request('http://worldclockapi.com/api/json/est/now', function(error,response,body){
if (!error && response.statusCode == 200)
result = body;
});
console.log(result);
});
I've tried to use callback but I'm confused to put the parameter, because actually this is also inside the callback.

Answer 1

request supports callback interfaces natively but does not return a promise. You must wait the asynchronous call to the external API is finished before sending back the response, and for this you should use a Promise which will resolves when the call to the API returns.
You can use the request-promise library and the rp() method which "returns a regular Promises/A+ compliant promise" and then, adapt your code as follows:
const functions = require('firebase-functions');
const rp = require('request-promise');
exports.getRequest = functions.https.onRequest((req, res) => {
let result = "this should be replaced";
var options = {
uri: 'http://worldclockapi.com/api/json/est/now',
json: true // Automatically stringifies the body to JSON
};
rp(options)
.then(parsedBody => {
result = parsedBody.currentDateTime;
console.log(result);
res.send( {result} );
})
.catch(err => {
// API call failed...
res.status(500).send({'Error': err});
});
});
I would suggest you watch the official Video Series (https://firebase.google.com/docs/functions/video-series/) which explains the key point about returning Promises and also how to handle errors in an HTTP Cloud Function.
Two extra points to note:
onRequest() arguments
You need to pass two arguments to the onRequest() function: the Request and theResponse` objects, see https://firebase.google.com/docs/functions/http-events?authuser=0#trigger_a_function_with_an_http_request
exports.date = functions.https.onRequest((req, res) => {
// ...
});
Pricing plan
You need to be on the "Flame" or "Blaze" pricing plan.
As a matter of fact, the free "Spark" plan "allows outbound network requests only to Google-owned services". See https://firebase.google.com/pricing/ (hover your mouse on the question mark situated after the "Cloud Functions" title)
Since the worldclock API is not a Google-owned service, you need to switch to the "Flame" or "Blaze" plan.

Answer 2

the callback calls asynchronous, so console.log(result) call before the callback run.
if you want to print the result variable with content from the requet you need to print it from the callback
const functions = require('firebase-functions');
const request = require('request');
exports.getRequest = functions.https.onRequest(() => {
let result = "this should be replaced";
request('http://worldclockapi.com/api/json/est/now', function(error,response,body){
if (!error && response.statusCode == 200)
result = body;
console.log(result);
});
});
however, I recommend request-promise and use async/await syntax
const functions = require('firebase-functions');
const request = require('request-promise');
exports.getRequest = functions.https.onRequest(async () => {
let result = "this should be replaced";
result = await request('http://worldclockapi.com/api/json/est/now');
console.log(result);
});