Secara amnya, Janji dikembalikan, dan ia mesti disimpan di mana sahaja ia digunakan.

UserBLL.GetByName = function(name) {
    return co(function() {
        return yield User.findOne({where: {username: name}})
    })
}

UserBLL.GetByName('xxx').then(function(res) {
    console.log(res)
})

UserBil.getByName = () => {
    var result = co.wrap(function* (){
        return request
        // something you want to return 
    })
    
    return result(true).then(function(value){
      return value
    })
}