JSON variable returns Undefined - node.js

Question

Sorry for the inconvenience, I am a newbie in Node. I am trying to store a json in "usersData" variable so I want to use it later in another functions. The problem is that if I test the variable with console.log inside the "if" it returns to me results, but when trying to show the variable outside the request subfunction, it comes out 'undefined'. I have declared the global usersData variable as shown below. Thank you.
var usersData;
function getAllUsers(){
request({url, json: true}, function (error, response, body) {
if (!error && response.statusCode == 200) {
usersData = body
//console.log(usersData) //Here returns a value
}
});
console.log(usersData) //here returns undefined
}

Answer 1

request is asynchronous method, so if you want to use its result later in another functions, should handle that in second parameter callback. i.e
var usersData;
var handleUserData = function() {};
function getAllUsers(){
request({url, json: true}, function (error, response, body) {
if (!error && response.statusCode == 200) {
usersData = body
//console.log(usersData) //Here returns a value
// use results in another function
handleUserData(body);
}
});
}
or use Promise
function getAllUsers() {
return new Promise(function(resolve, reject) {
request({url, json: true}, function (error, response, body) {
if (!error && response.statusCode == 200) {
usersData = body
//console.log(usersData) //Here returns a value
resolve(body);
} else {
reject(error);
}
});
});
}
// handle `usersData`
getAllUsers().then(body => {
handleUserData(body);
});

Answer 2

Here are some stuffs you need to know,
request is a asynchronous function which means it runs on background without blocking main thread, so the callback function is executed after the request completes, that is why value of body is assigned to userData and when printed gives some value.
But when printing outside of the callback function, it gives undefined because of request being async takes time to complete which run on background. So, consoling statement runs before the body is assigned to userData and so when printed gives undefined.