javascript - How to avoid callback hell in this scenario? -


i have following code can see, each of functions inside functions rely on return value of enclosing function. problem when keep using method code, callback hell occurs. how avoid 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            })        }    })

the model file follows

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 `user` `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 `user` `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 `user_detail` `user_id` = ?', id, function(err, rows, fields) {         callback(rows)     }) }

i'm using code in production website. how can transition callback hell structured code?

use javascript promises

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

can made

q.fcall(promisedstep1) .then(promisedstep2) .then(promisedstep3) .then(promisedstep4) .then(function (value4) {     // value4 }) .catch(function (error) {     // handle error above steps })

read more here link q.js


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