node.js - NodeJS - Q - How to pass a promise in another promise -

i want return or pass promise promise don't know how that. codes:

function seedusers(){     var def = q.defer();      _seedusersindb(function(err, users){         if(err){             return def.reject(err);         }         def.resolve(users);     })      return def.promise; }  function seeddb(){     var def = q.defer();      _checkcountofusers(function(count){         if(count > 0){             // seeded             return def.resolve();         } else{             // have use seedusers()              // ????????????????????             // how pass seedusers() ????             // ????????????????????         }     })      return def.promise; } 

what codes put in specified section? thanks

mixing promisified , unpromisified functions messy, therefore promisify both low level functions :

// promisify _seedusersindb() function _seedusersindbasync() {     var def = q.defer();     _seedusersindb(function(err, users) {         if(err) def.reject(err);         else def.resolve(users);     });     return def.promise; }  // promisify _checkcountofusers() function _checkcountofusersasync() {     var def = q.defer();     _checkcountofusers(function(err, count) {         if(err) def.reject(err);         else def.resolve(count);     });     return def.promise; } 

now, nodebacks disappear higher level code, in favour of promise chains.

function seeddb() {     return _checkcountofusersasync.then((count) => {         return (count > 0) ? count : _seedusersindbasync().then((users) => users.length);     }); }