javascript - Undefined arguments using async.apply inside of async.series -

i using async library inside of project , end strange behavior : of arguments "undefined" in call.

for example (this not actual code behavior same , simpler expose problem way) :

var token;  async.series([     function gettoken (done) {         api.gettoken(userid, function (err, data) {             if (err) return done(err);             token = data;             return done();         }     },     async.apply(dosomethingwiththetoken, token) ], callback); 

when function "dosomethingwiththetoken" called, token passed argument has "undefined" value, if changed in previous function "gettoken".

but if :

var token;  async.series([     function gettoken (done) {         api.gettoken(userid, function (err, data) {             if (err) return done(err);             token = data;             return done();         }     },     function dosomething (done) {         dosomethingwiththetoken(token, done);     } ], callback); 

then no problem token passed in function "dosomethingwiththetoken" has correct value given previous function.

i've done little bit of research in async module before writing post , when display arguments passed async.apply function, surprise displayed before function call made in async.series flow - explains why token value "undefined".

is able explain me why behavior happening ?

i hope i've been clear issue in advance

whenever async.series called, prepares function references within array, adds gettoken in array, calls async.apply , adds generated function reference (output of async.apply) in array.

at time token undefined.

scenarios happening here this:

> var i;  > var arr = [1,2,3,i,5,6];  > i=4;  > arr [ 1, 2, 3, undefined, 5, 6 ] 

hope understand this.