Example using async library to avoid callback hell

controlAsyncFlow.js

var async = require('async');
var Product = require('../model/Product');
var Category = require('../model/Category');
var Attribute = require('../model/Attributes');

// bad idea
exports.index = function() {
  Product.find(function(err, products) {
    Category.find(function(err, categories) {
      Attribute.find(function(err, attributes) {
        res.render('index', {
          products: products,
          categories: categories,
          attributes: attributes
        });
      })
    });
  });
};

// good idea
exports.index = function() {
  var getProducts = function(cb) {
    Product.find(function(err, products) {
      cb(null, products)
    });
  };
  
  var getCategories = function(cb) {
    Category.find(function(err, categories) {
      cb(null, categories);
    });
  };
  
  var getAttributes = function(cb) {
    Attribute.find(function(err, attributes) {
      cb(null, attributes);
    });
  };
  
  var renderIndex = function(err, data) {
    res.render('index', {
      products: data.products,
      categories: data.categories,
      attributes: data.attributes
    });
  };
  
  async({
    products: getProducts,
    categories: getCategories,
    attributes: getAttributes
  }, renderIndex);
};