node.js - Extract data from variables inside multiple callbacks in javascript -

i'm ok javascript , callbacks, i'm getting annoyed @ , need call on the world of stackoverflow help.

i have written function, used in following way:

var meth = lib.function(a,b); // meth should hold array of properties { c, d } once executed 

so inside lib.js, have structure like:

exports.function = function (a,b) {     database.connect(params, function(err,get){           get.query(querylang, function(err, results){                  var varsiwanttoreturn = { var1: results[i].foo, var2: results[i].bar };           });     }); // how return 'varsiwanttoreturn'? }; 

i have seen things incorporating callback() function, i'm not sure how works. i've seen people use exec() - again, im not sure on how or why use it.

please :) in advance.

well, it's asynchronous if attempt return - it'll return undefined. in javascript (sans new yield keyword) functions execute top bottom synchronously. when make io call database call - still executes synchronously. in fact- when variwanttoreturn gets population function has long run , terminated.

what left same thing async functions database.connect , get.query , have function take callback:

exports.function = function (a,b, callback) {     database.connect(params, function(err,get){           if(err) return callback(err, null); // don't suppress errors           get.query(querylang, function(err, results){                if(err) return callback(err, null); // don't suppress errors                var varsiwanttoreturn = { var1: results[i].foo, var2: results[i].bar };                callback(null, varsiwanttoreturn);          });     }); }; 

then you'd call like

myexportedfunction(mya,myb, function(err, resp){     if(err) recoverfromerror(err);     // varsiwanttoreturn contained in `resp` });