Nicer callback Javascript code in Express/NodeJs

Question

Nicer callback Javascript code in Express/NodeJs

function DatabaseConnect(req, res) {...}
function CreateNewUser(req, res) {...}

function Go (app, req, res) {

    // If is POST on this URL run this function
    var firstFunction = app.post('/admin/svc/DB', function(res, req) { 
        DatabaseConnect(req, res) 
    });

    // If is POST on this URL run this function
    var secondFunction = app.post('/admin/svc/CREATE', function(res, req) { 
        CreateNewUser(req, res) 
    });

    // Run first all callbacks and after render page
    function Render(firstMe, afterMe) {
        firstMe();
        afterMe();
        app.render('screen');
    }

    Render(firstFunction, secondFunction);

}

Go();

How can I run more functions asyn. and Render() after all?

APP.POST is called if ist POST on that URI.

javascript
node.js
asynchronous
routing
express

Answer 1

There are various different approaches here, depending on your needs. If you just care about a set number of async functions completing, one common pattern is to basically maintain a count and fire the afterAll() method when you're done:

var count = 0,
    target = 2; // the number of async functions you're running

function afterAll() {
    if (++count === target) {
        // do something
    }
}

doAsync1(function() {
    // some stuff
    afterAll();
});

doAsync2(function() {
    // some stuff
    afterAll();
});

Underscore offers a couple of useful utilities here, including _.after:

var asyncMethods = [doAsync1, doAsync2, doAsync3],
    // set up the callback to only run on invocation #3
    complete = _.after(asyncMethods.length, function() {
        // do stuff
    });
// run all the methods
asyncMethods.forEach(function(method) {
    // this assumes each method takes a callback
    method(complete);
});