The good/bad promise examples

good_bad_promises.js

// Idea 1: http://www.datchley.name/promise-patterns-anti-patterns/

// good
good();

function good() {
    // getJSON returns a promise, so just continue the chain 
    return getJSON()
        .then(function (artists) {
            // Map the array of artists to an array of names
            return artists.map(function (artist) {
                return artist.name;
            });
        })
        .then(function (names) {
            // This could have been in the "thenable" before, but
            // it's best functions only do one thing and do it well
            console.log('(good) The promise was resolved::', names);
        })
        .catch(function (err) {
            console.log('(good) The promise was rejected::', err);  
        })
}

// bad
bad();

function bad() {
    // Create a new promise and resolve/reject when
    // the getJSON is resolved or rejected
    return new Promise(function (resolve, reject) {
        getJSON()
            .then(function (artists) {
                // Map the array of artists to an array of names
                var names = artists.map(function (artist) {
                    return artist.name;
                });
                
                // The "thenable" is doing too much
                resolve(names);
                console.log('(bad) The promise was resolved::', names);
            })
            .catch(function (err) {
                reject(err)
                console.log('(bad) The promise was rejected::', err);
            });
    });
}

// A wrapper that returns a promise which is
// resolved with an array of artist objects. Lets assume
// that this might also throw an error (even though it doesn't')
function getJSON() {
    return Promise.resolve([{
        id: 1,
        name: 'Jay-Z'
    }, {
        id: 2,
        name: 'Kanye West'
    }, {
        id: 3,
        name: 'Meshuggah'
    }]);
}