Here we're chaining multiple promises, which solves the callback hell.

promise_example2.js

/**
 * This function returns a promise to fetch a user by id
 */
function getUserWithId(id) {
    return new Promise((resolve, reject) => {
        // Look for a user with id in the database
        User.find({_id: id}, (user, err) => {
            if(err) return reject(err);

            // on success
            resolve(user); // from pending --> resolved
        });
    });
}

/**
 * This function returns a promise to fetch a list of friends
 */
function getUserWithFriends(id) {
    return new Promise((resolve, reject) => {
        // Look for a user with id in the database
        Friends.find({friends.id: id}, (friends, err) => {
            if(err) return reject(err);

            // on success
            resolve(friends); // from pending --> resolved
        }
    });
}
                       
function getUserImage(url) {
    return new Promise((resolve, reject) => {
        // Look for a user with id in the database
        http.get({link: url}, (image, err) => {
            if(err) return reject(err);

            // on success pass the image
            resolve(image);
        });
    });
}
    
/**
 * Chaininig promises :)
 */
getUserWithId(someId)
    .then(user => getUserWithFriends)
    .then(friends => getUserImage(url))
    .then(image)
    .catch(ex => {
        // send or throw an error   
    });