Node.js: How to run asynchronous code sequentially

Question

I have this chunk of code

User.find({}, function(err, users) {
    for (var i = 0; i < users.length; i++) {
        pseudocode
        Friend.find({
              


        

Answer 1

I prefer the promise module to q https://www.npmjs.com/package/promise because of its simplicity

var Promises = require('promise');
var promise = new Promises(function (resolve, reject) {
    // do some async stuff
    if (success) {
        resolve(data);
    } else {
        reject(reason);
    }
});
promise.then(function (data) {
    // function called when first promise returned
    return new Promises(function (resolve, reject) {
        // second async stuff
        if (success) {
            resolve(data);
        } else {
            reject(reason);
        }
    });
}, function (reason) {
    // error handler
}).then(function (data) {
    // second success handler
}, function (reason) {
    // second error handler
}).then(function (data) {
    // third success handler
}, function (reason) {
    // third error handler
});

As you can see, you can continue like this forever. You can also return simple values instead of promises from the async handlers and then these will simply be passed to the then callback.