Clean Express controllers using currying and promises

README.md

Purpose

Demonstrate how to write clean express controllers using function currying and promises.

• Promises helps avoiding callback hell
• Currying helps code reuse

Install, run, test

git clone https://gist.github.com/8472f35350a7031e2cb2.git express_curry_promise
cd express_curry_promise
npm install
node app.js

... in another shell

curl -v http://localhost:3000/flip/head
curl -v http://localhost:3000/flip/tail
curl -v http://localhost:3000/flip/head
curl -v http://localhost:3000/flip/tail

app.js

var express = require('express');
var app = express();

var flipController = require('./flip_controller');

app.get('/flip/:bet', flipController.get);

app.listen(3000);

flip_coin.js

var Promise = require('bluebird'); // Awesome promise library

module.exports = function(bet){

  var result = Math.round(Math.random()) ? 'head' : 'tail';

  var responder = result === bet.toLowerCase() ? Promise.resolve : Promise.reject;

  return responder({
    success: result === bet,
    bet: bet,
    result: result
  });
};

flip_controller.js

var _ = require('lodash'); // underscore++
var flipCoin = require('./flip_coin'); // Your actual handler, usually async

var respond = _.curry(function(res, status, payload){
  console.log('responding [%s] result:', status, payload);
  res.status(status).send(payload).end();
});

var controller = {
  get: function(req, res){
    var bet = req.params.bet;

    if(
      typeof bet !== 'string' || (
        bet.toLowerCase() !== 'head' &&
        bet.toLowerCase() !== 'tail'
      )
    ){
      respond(res, 400, {
        message: 'missing or incorrect parameter `bet`, expects "head" or "tail" string'
      });
      return;
    }

    flipCoin(bet)
      .then(respond(res, 200)) // on success, send a 200 and forward flipCoin result
      .catch(respond(res, 403));// on error, send a 403 and forward flipCoin result
  }
}

module.exports = controller;

package.json

{
  "name": "curry_promise_express",
  "version": "1.0.0",
  "description": "Example of clean Express controllers using currying and promises",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "repository": {
    "type": "git",
    "url": "https://gist.github.com/8472f35350a7031e2cb2.git"
  },
  "keywords": [
    "curry",
    "express",
    "promise"
  ],
  "author": "Arnaud Rinquin",
  "license": "MIT",
  "dependencies": {
    "bluebird": "^2.3.6",
    "express": "^4.9.8",
    "lodash": "^2.4.1"
  }
}