How do I use async in node.js - arrays

Question

I have created a code in node.js, which use mongoDB. Everything is working fine, but when I use nested loop, it break and don't return the proper values.
DB1.find({},function(error,fetchAllDB1) {
var mainArray = new Array();
for (var i in fetchAllDB1) {
if(fetchAllDB1[i].name) {
var array1 = new Array();
var array2 = new Array();
array1['name'] = fetchAllDB1[i].name;
array1['logo'] = fetchAllDB1[i].logo;
array1['desc'] = fetchAllDB1[i].desc;
DB2.find({is_featured:'1', brand_id: fetchAllDB1[i]._id}, function(error,fetchDB2) {
for (var p in fetchDB2) {
var pArr=[];
pArr['_id'] = fetchDB2[p]._id;
pArr['name'] = fetchDB2[p].name;
pArr['sku'] = fetchDB2[p].sku;
pArr['description'] = fetchDB2[p].description;
console.log('>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>');
console.log(pArr);
console.log('<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<');
array2[p]=pArr;
}
array1['pp']= array2;
});
mainArray[i]=array1;
}
}
console.log('######### LAST #########');
console.log(mainArray);
console.log('######### LAST #########');
});
In my console message its showing
console.log('######### LAST #########');
All Values
console.log('######### LAST #########');
After that
console.log('>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>');
All Values;
console.log('<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<');
I want to use async in my code, so that all data fetching occur as below:
mainarray =
[
[array1] = All Values
[array2] = [0]
[1]
]
mainarray =
[
[array1] = All Values
[array2] = [0]
[1]
]

Answer 1

Your code is very confusing and overly complicated.
What you should do is (psuedo code):
DB1.find(foo) // returns one result
.then(getFromDB2);
function getFromDB2 (res){
return DB2.find(res); // make a query here with mongo drivers `$in`
}
Mongodb : $in operator vs lot of single queries