lecture04-notes.md

Chaining promises

database.js

let databaseModule = {
    getUser,
    getUserEmail
};

let users = [
    {
        firstName: 'Spruce',
        lastName: 'Feinstein'
    },
    {
        firstName: 'John',
        lastName: 'Snow'
    },
    {
        firstName: 'Leslie',
        lastName: 'Palmer'
    },
    {
        firstName: 'Alex',
        lastName: 'Martinez'
    }
];

let emails = [
    {
        firstName: 'Spruce',
        email: '[email protected]',
    },
    {
        firstName: 'John',
        email: '[email protected]',
    },
    {
        firstName: 'Leslie',
        email: '[email protected]',
    },
    {
        firstName: 'Alex',
        email: '[email protected]',
    }
];

function getUser(firstName) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            for (let i = 0; i < users.length; i++) {
                if (users[i].firstName === firstName) {
                    return resolve(users[i])
                }
            }
            return reject('user not found');
        }, 200);
    });
}

function getUserEmail(userFirstName) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            for (let i = 0; i < emails.length; i++) {
                if (emails[i].firstName === userFirstName) {
                    return resolve(emails[i].email)
                }
            }
            return reject('email not found');
        }, 200);
    });
}

module.exports = databaseModule;

app.js

let database = require('./module');

database.getUser('Spruce')
.then((user) => {
    console.log(user);
    return database.getUserEmail(user.firstName);
})
.then((userEmail) => {
    console.log(userEmail);
})
.catch((err) => {
    console.log(err);
});

Promise.all

app.js

let database = require('./module');


let userPromises = [];

userPromises.push(database.getUser('Spruce'));
userPromises.push(database.getUser('Spruce'));
userPromises.push(database.getUser('Spruce'));
userPromises.push(database.getUser('Spruce'));

Promise.all(userPromises)
.then((data) => {
    console.log(data);
});