javascript - How to simplify deep nested promises -

i have come across situation need break @ every "else" clause in then(), , doesn't better nested callbacks, login process:

user.findone({     username: username }).exec()     .then(user => {         if (user) {             return user.verifypassasync()                 .then(matched => {                     if (matched) {                         return user.getbriefprofile(username))                             .then(emp => {                                 if (emp) {                                     return savetosession(emp);                                 } else {                                     //return                                  }})                     } else {                         //return ...                     }})         } else {         // return false         }     }) 

is there way can simplify this?

not really, you're not (only) nesting promises here rather conditionals. if written async/await (es7), function like

var user = await user.findone({username}).exec(); if (user) {     var matched = await user.verifypassasync();     if (matched) {         var emp = await user.getbriefprofile(username);         if (emp) {             return savetosession(emp);         } else {             // return …;         }     } else {         // return …;     } } else {     // return …; } 

as can see, nesting inherent program. it's bit simplified though (no nesting then calls), , can right promise.coroutine , es6 generators.

your best bet might throw error in each else, , linearise chain that, .catching in end. of course, if doing same thing in each else block, write

var user = await user.findone({username}).exec(); if (user)     var matched = await user.verifypassasync(); if (matched)     var emp = await user.getbriefprofile(username); if (emp) {     return savetosession(emp); else     // return …; 

which translates then callbacks:

user.findone({username: username}).exec() .then(user =>     user && user.verifypassasync() ).then(matched =>     matched && user.getbriefprofile(username); ).then(emp =>     emp ? savetosession(emp) : …; );