javascript - 在这种情况下如何避免回调 hell ？

Question

如您所见，我有以下代码，函数内的每个函数都依赖于封闭函数的返回值。但问题是当我继续使用这种方法编码时，就会出现回调 hell 。如何避免这个 hell ？

User.getUserDetail(req.user.id, function(userDetail) {
       if(req.user.entity_id != '-1') {
           Entity.getEntityPrimary(req.user.entity_id, function(entityPrimary) {
               Entity.getEntityPayment(req.user.entity_id, function(entityPayment) {
                   if(entityPayment.length > 0) {
                       Entity.subscriptionInfo(entityPayment[0]['date'], entityPayment[0]['exp_date'], function(isSubscribed) {
                           res.render('capitol', {
                               user: req.user,
                               title: 'MCIC',
                               user_detail: userDetail,
                               entity_primary: entityPrimary,
                               entity_payment: entityPayment,
                               subscriber: true,
                               is_subscribed: isSubscribed
                           })
                       })
                   } else {
                       res.render('capitol', {
                           user: req.user,
                           title: 'MCIC',
                           user_detail: userDetail,
                           entity_primary: entityPrimary,
                           entity_payment: entityPayment,
                           subscriber: false
                       })
                   }
               })
           })
       } else {
           res.render('capitol', {
               user: req.user,
               title: 'MCIC',
               user_detail: userDetail
           })
       }
   })

模型文件如下

const MySql = require('../comms/mysql')
const User = module.exports = {}

User.getUserByUsername = function(username, callback) {
    MySql.connection.query('SELECT id, username, password, is_active, email, mobile, user_type_id, entity_id FROM `user` WHERE `username` = ?', username, function(err, rows, fields) {
        callback(rows)
    })
}

User.getUserById = function(id, callback) {
    MySql.connection.query('SELECT id, username, password, is_active, email, mobile, user_type_id, entity_id FROM `user` WHERE `id` = ?', id, function(err, rows, fields) {
        callback(err, rows)
    })
}

User.getUserDetail = function(id, callback) {
    MySql.connection.query('SELECT first_name, last_name, dob, address_no, address_street, address_district, address_postal_code, profile_picture, user_id FROM `user_detail` WHERE `user_id` = ?', id, function(err, rows, fields) {
        callback(rows)
    })
}

我在生产网站中使用此代码。如何轻松地从回调 hell 过渡到结构良好的代码？

Answer 1

使用 JavaScript promise

step1(function (value1) {
    step2(value1, function(value2) {
        step3(value2, function(value3) {
            step4(value3, function(value4) {
                // Do something with value4
            });
        });
    });
});

可以制作

Q.fcall(promisedStep1)
.then(promisedStep2)
.then(promisedStep3)
.then(promisedStep4)
.then(function (value4) {
    // Do something with value4
})
.catch(function (error) {
    // Handle any error from all above steps
})

在此处了解更多信息 Link to Q.js