program.js

function loadUsers(userIds, load, done) {
    var completed = 0;
    var users = [];
    userIds.forEach(function(id, index) {
        load(id, function(user) {
            users[index] = user;
            if (++completed === userIds.length)
                return done(users);
        })
    })
}

module.exports = loadUsers;