javascript - callback returns value but apears to be undefined -

i new node , callbacks. trying split list of groups array. groups seperated comma's or "-". last 1 means interval if there 22-25 means: 22, 23, 24, 25. tried following code.

var groups = ["13-16","21-24","33"]; var splitgroups = function(groups, callback){    var result = [];    console.log(groups.length);    for(var i=0; i<groups.length; i++){      var cbr = callback(groups[i]);      result = result.concat(cbr);    }   return result; }  var handlegroupinterval = function(group){   var temparr = [];   try {     temparr = group.split('-');   }   catch(err) {     console.log(err.message);   }   console.log("groups split: "+group);   if(temparr.length>1){       var lowerbound = parseint(temparr[0]);       var upperbound = parseint(temparr[1]);         temparr = [];       for(var j=lowerbound; j<=upperbound; j++){         temparr.push(j);       }     }       return temparr; } var tempgroups = splitgroups(groups, function(res){handlegroupinterval(res)}); console.log("end: " +tempgroups); 

when set breakpoint on "return temparr" proper values. in first function result thee times undefined. knows problem?

you not return callback.

simply replace

var tempgroups = splitgroups(groups, function(res){handlegroupinterval(res)}); 

with

var tempgroups = splitgroups(groups, function(res){ return handlegroupinterval(res); }); 

notice added return in callback.

also, think further simplify as

var tempgroups = splitgroups(groups, handlegroupinterval);