javascript - Calling another prototype method after promise completed -

i have following code in node.js file;

gamehelperauth.prototype.getuserviaapi = promise.method(function (authcookie, callback) { // user api });  gamehelperauth.prototype.getobjectfromcache = promise.method(function (authcookie, callback) { // user cache });  gamehelperauth.prototype.getuser = function (authcookie, callback) {         // check cache         this.getobjectfromcache()         .then(function (result) {             if (result) {                 return callback(null, result);             }             else {             // not found in cache, api             // **not working here - undefined error**                 this.getuserviaapi(authcookie)                     .then(function (apiresult) {                         return callback(null, apiresult);                     }).catch(function (err) {                         throw err;                     });             }         })         .catch(function (err) {             throw err;         }); 

i access instance method instance method once promise completed. looks loses it's context , cannot find function anymore. (please see calling getuserviaapi method)

is there way me reach method without creating new instance of class?

as far can see, simplest fix here declare var self = this in first line of .getuser() , use self instead of this inside .then callback.

alternatively if you're using node 4+ es6 compatibility, use "arrow function" outer .then callback inherits lexical this instead of contextual this:

return this.getobjectfromcache()     .then((result) => {         if (result) {             return callback(null, result);         } else {             // not found in cache, api             return this.getuserviaapi(authcookie)                 .then(function (apiresult) {                     return callback(null, apiresult);                 }).catch(function (err) {                     throw err;                 });         }     })     .catch(function (err) {         throw err;     }); 

nb: note addition of return in first line , in else clause, necessary ensure function , branch both correctly return promise.

fwiw, think can refactor substantially eliminating repeated call return callback(...) through chaining .then:

gamehelperauth.prototype.getuser = function (authcookie, callback) {    return this.getobjectfromcache()        .then(result => result || this.getuserviaapi(authcookie))        .then(result => callback(null, result)); } 

i've removed both .catch blocks - doing .catch(function(err) { throw err }) no-op - aiui throw make caller end in own .catch block might let entire promise reject anyway.