How to use the values of a POST response in Node.js? - node.js

Question

I am setting up an API connection via Node.js. I had some predefined cURL code which I converted into Node.js code, which I have provided below. Until now everything works fine, I am displaying the value I need (token) inside the console window.
However, I am wondering how I can use this token variable in another function? So I somehow have to save it as a global variable, but until now that didn't work.
var request = require('request');
var headers = {
'content-type': 'application/x-www-form-urlencoded',
'Authorization': 'XXXXXXXXXXXXXXXXX'
};
var dataString = 'grant_type=client_credentials';
var options = {
url: 'XXXXXXXXXXXXXXXX',
method: 'POST',
headers: headers,
body: dataString
};
function callback(error, response, body) {
if (!error && response.statusCode == 200) {
var str = body;
token = str.split('\"')[3];
console.log(token);
}
}
request(options, callback);

Answer 1

You can access token only when request() complete and calls the callback function. This is due to the non-blocking nature of node.js - when you start a request the code doesn't block and you can access its response only when it completes and call the callback function. Hence you first define the callback function and pass it to request as an argument. If you want to access token you can create another function and call it inside the callback.
var request = require('request');
var headers = ...
var dataString = ...
var options = ...
function doStuffWithToken(token) {
console.log(token)
}
function callback(error, response, body) {
if (!error && response.statusCode == 200) {
var str = body;
token = str.split('\"')[3];
doStuffWithToken(token);
}
}
request(options, callback);
You can also use promises for better code:
var request = require('request');
function getToken() {
var headers = ...
var dataString = ...
var options = ...
return new Promise((resolve, reject) => {
request(options, (error, response, body) => {
if (error) return reject(error)
if (response.statusCode == 200) {
var str = body;
token = str.split('\"')[3];
resolve(token);
}
}
}
}
getToken()
.then((token) => {
// here you can access the token
console.log(token)
})
.catch((error) => {
console.error('unable to retrieve token', error)
})
Here we create a wrapper around our request. getToken() returns a promise object that you can use to register two handlers for when it resolves successfully and for when it rejects and throw an error.
You can use getToken() also with the await/async keyword
var request = require('request');
function getToken() {
var headers = ...
var dataString = ...
var options = ...
return new Promise((resolve, reject) => {
request(options, (error, response, body) => {
if (error) return reject(error)
if (response.statusCode == 200) {
var str = body;
token = str.split('\"')[3];
resolve(token);
}
}
}
}
async function main() {
let token = await getToken()
console.log(token)
}
main()
.then(...)
.catch(...)
Further readings:
Don't block the event loop