nodejs loop async callback function - node.js

Question

I am running a cron job with node with mongodb as the database. I am trying to close db connection and exit the process once the curr_1 each loop has executed completely.
However the exit() is called while function_2 is being executed. I understand this is due to the callback and is async in nature.
How do I make sure exit is called only once the curr_1.each is complete?
Any solution without promises?
function function_1(obj){
var curr_1 = coll_1.find({})
curr_1.each(function(err, doc) {
function_2(doc)
});
exit(obj)
}
function function_2(obj) {
coll_2.findOne({}, function(err, document) {
dosomeprocess(obj)
})
}
function exit(obj) {
// Close connection
console.log('closing connection')
obj.db.close();
process.exit();
}

Answer 1

It's a job for Node async....
For example:
async.each(
curr_1, // the collection to iterate over
function(doc, callback) { // the function, which is passed each
// document of the collection, and a
// callback to call when doc handling
// is complete (or an error occurs)
function_2(doc);
},
function(err) { // callback called when all iteratee functions
// have finished, or an error occurs
if (err) {
// handle errors...
}
exit(obj); // called when all documents have been processed
}
);

Answer 2

Without using any library:
function function_1(obj, callback) {
var curr_1 = coll_1.find({})
curr_1.each(function(err, doc) {
callback(err, doc);
});
}
function function_2(err, obj) {
coll_2.findOne({}, function(err, document) {
dosomeprocess(obj)
exit(err, obj);
})
}
function exit(err, obj) {
// Close connection
console.log('closing connection')
obj.db.close();
process.exit();
}
function_1(obj, function_2);
Using async module
var async = require('async');
async.waterfall([
function function_1(callback) {
var curr_1 = coll_1.find({})
curr_1.each(function(err, doc) {
if (err) {
callback(err, null)
} else {
allback(null, doc)
}
});
},
function function_2(obj, callback) {
coll_2.findOne({}, function(err, document) {
if (err) {
callback(err, null);
} else {
dosomeprocess(obj)
callback(null, obj);
}
})
}
], function done() {
obj.db.close();
process.exit();
});

Answer 3

Simply give a condition in your loop using counter.
function function_1(obj){
var curr_1 = coll_1.find({})
var curr_1Length = curr_1.length;
var counter = 0;
curr_1.each(function(err, doc) {
++counter;
//Check condition everytime for the last occurance of loop
if(counter == curr_1Length - 1){
exit(obj)
}
function_2(doc)
});
}
Hope it helps :)