javascript - how to pass promise to map -

i have blog , i've posts on it.
in post table inserted posts authorid. , want convert authorid authorname table called user.
convert, use function getpostauthor returns promise main function.
can't collect returned value getpostauthor map function
problem?

var db = require('../controllers/db'); var mongo = require('mongodb').mongoclient();  var url = "mongodb://localhost:27017/blog"; var objectid = require('mongodb').objectid;   //#1: function lists posts in blog const list = function(req, res){     db.find('post', {}, 10, {timecreated: 1})     .then(posts => {         var promises = posts.map(post =>             getpostauthor(post.author)             .then(author => author /* value doesn't go promises*/)         );         console.log(promises); //printed [promise {<pending>}, ...]     }) }  //#2: function gets authorid , gives authorname const getpostauthor = function(authorid){     return db.findone('user', {_id: new objectid(authorid)})     .then(author => author.name); }  //#3: finds db const find = function(collection, cond = {}, limit = 0, sort = {}){         return mongo.connect(url)         .then(db =>             db.collection(collection)             .find(cond)             .limit(limit)             .sort(sort)             .toarray()         ) }   //#4: finds 1 db const findone = function(collection, cond = {}){         return mongo.connect(url)         .then(db =>             db.collection(collection).findone(cond)         ) }   list(); 

you need wait promises received using .map resolve see values - this:

const list = function(req, res){     db.find('post', {}, 10, {timecreated: 1})     .then(posts => {         var promises = posts.map(post =>             getpostauthor(post.author)             .then(author => author /* value doesn't go promises*/)         );         console.log(promises); //printed [promise {<pending>}, ...]         // ********* 3 lines added code here         promise.all(promises).then(authors => {             console.log(authors);         });     }) } 

alternatively

const list = function(req, res){     // added return below     return db.find('post', {}, 10, {timecreated: 1})     .then(posts => {         var promises = posts.map(post =>             getpostauthor(post.author)             .then(author => author /* value doesn't go promises*/)         );         console.log(promises); //printed [promise {<pending>}, ...]         // *** added line below         return promise.all(promises);     }) } 

...

list().then(authors => {     console.log(authors); });