other experiment ideas

app.js

/**
 * Module dependencies
 */
var express = require("express")
  , experiments = require("./experiments");
 
var app = module.exports = express();

/**
 * Features
 */
// Defaults to [true, false]
experiments.feature("validate");
// Multi-variant
experiments.feature("loginButtonColor", ["red", "blue", "green", "yellow"]);

/**
 * Configure our app
 */
app.configure(function(){
  app.use(experiments);
});
 
app.get("/", function(req, res, next){
  res.render("view");
});
 
app.get("/ad-hoc", function(req, res, next) {
  // We can do ad-hoc features
  res.feature("welcomeMessage", ["message1", "message2"], function(err) {
    if(err) return next(err);
    
    if(res.features.validate) {
      // Our validate feature is turned on
    }
    else {
      // It's turned off
    }
    
    res.render("view");
  }); 
});

experiment.js

/**
 * Module dependencies
 */
var pivot = require("pivot");

/**
 * Expose experiments
 */
var experiments = module.exports = pivot();

/**
 * Store the user's enabled features
 */
experiments.serialize(function(features, req, res, next){
  res.cookie("pivot", JSON.stringify(features));
  next();
});

/**
 * Get the enabled features for the user
 */
experiments.deserialize(function(req, res, next){
  next(null, JSON.parse(req.cookies.pivot));
});

/**
 * Gives the user object to pivot
 */
experiment.findUser(function(req, res, next){
  next(null, req.user);
});

/**
 * Retrieve feature settings from our backend
 * 
 * This can be anything:
 * * JSON file
 * * API Call (i.e. Product owner service)
 * * DB Call
 * 
 * These should really be separate modules so you can have pluggable backends to do this stuff
 */
experiments.lookup(function(){
  var features = {};
  
  /**
   * @param {String} name
   * @param {Array[String]} variants
   * @param {Function} done
   */
  return function(name, variants, done){
    /**
     * We can do a few things here:
     * * Lookup our feature settings locally
     * * If we dont have it, notify the admin control panel page
     * * Log outdated features; either ones that should be integrated or ones that should be removed
     */
   
    // In this case we'll just look it up locally
    
    // This should also look up if the variants have changed
    if(features[name]) {
      done(null, features[name]);
    }
    else {
      var feature = features[name] = {};
      variants.forEach(function(variant) {
        // Give it an equal split by default (expects 0 to 1)
        feature[variant] = 1/variants.length;
        
        // We could also give it a list of groups
        //   feature[variant] = ["beta", "admins"];
        
        // or just a single group
        //   feature[variant] = "beta";
      });
      
      done(null, features[name]);
    }
  };
})());

/**
 * Tells pivot which variant gets assigned to the user
 *
 * @param {String} feature
 * @param {Object} variants
 * @param {Object} user
 * @param {Function} done
 */
experiments.assign(function(feature, variants, user, done){
  /**
   * If the variant is a group, we can inspect the `user` object to check where they fall
   * If the variant is a weight, we can implement our own random assignment algorithm
   *
   * The callback expects the name of the variant chosen for the given user
   */

  // For this example we're just going to assign the first variant to everyone
  done(null, Object.keys(variants)[0]);
});

view.ejs

<h1>
  <% switch(features.welcomeMessage){ %>

    <% case "message1": %>
      "Welcome!"
    <% break; %>

    <% case "message2": %>
      "Hey there Friend!"
    <% break; %>

  <% } %>
</h1>

<div class="login">
  <button class="btn btn-<%= features.loginButtonColor %>">Login</button>
</div>

view.nghtml

<div class="login" data-pivot="'loginButtonColor'">
  <button data-pivot-vary="'red'" class="btn btn-red">Login</button>
  <button data-pivot-vary="'blue'" class="btn btn-blue">Login</button>
</div>

The only view engines that would work with this setup are async ones