Demystification of functions in sequelizejs

isitclearnoworwhat.js

/**
 * Old version
 */
return sequelize.transaction(function (t) {
    return User.create({
        firstName: 'Abraham',
        lastName: 'Lincoln'
    }, {transaction: t}).then(function (user) {
        return user.setShooter({
            firstName: 'John',
            lastName: 'Boothe'
        }, {transaction: t});
    });
}).then(function (result) {
    // Transaction has been committed
    // result is whatever the result of the promise chain returned to the transaction callback 
}).catch(function (err) {
    // Transaction has been rolled back
    // err is whatever rejected the promise chain returned to the transaction callback
});


/**
 * New version
 */
var newUser = {
    firstName: 'Abraham',
    lastName: 'Lincoln'
};
var shooter = {
    firstName: 'John',
    lastName: 'Boothe'
};

return sequelize.transaction(createUser(t))
    .then(complete(result))
    .catch(rollBack(err));

function createUser (t) {
    return User.create(newUser, {transaction: t})
        .then(setShooterForUser(user));
}

function setShooterForUser (user) {
    return user.setShooter(shooter, {transaction: t});
}

function rollBack (err) {
    // Transaction has been rolled back
    // err is whatever rejected the promise chain returned to the transaction callback
}

function complete (result) {
    // Transaction has been committed
    // result is whatever the result of the promise chain returned to the transaction callback 
}