XPR-Express.js

This is a Node.js plugin for XPRMNTL feature-client. It adds the ability to call req.feature from within an express.js app. req.feature('expName') returns the value of the feature.

Installation

$ npm install xpr-express

API

var featureClient = require('feature-client');
var xprExpress = require('xpr-express');
var app = require('express')();
var cookieParser = require('cookie-parser');

featureClient.use(xprExpress());
app.use(cookieParser());
app.use(featureClient.express);

app.get('/', function() {
  if (req.feature('featureName')) {
    // Do something with feature on
  } else {
    // Do something for feature off
  }
});

xprExpress(config)

• config.cookieName is used if no readExps/saveExps are defined. Feature configuration is stored in the user's cookie as needed.

• config.readExps is a function with the following footprint:

  Defaults to reading an experiment cookie (config.cookieName)

  function(req, res) {
    // read experiment data from express `req` and `res` or other means
    return experiments; // see Experiment Format
  }

• config.saveExps is a function with the following footprint:

  Defaults to writing an experiment cookie (config.cookieName)

  function(userID, experiments, res) {
    // Save experiment configuration to express `res` or other means
  
    return; // nothing
  }

• Experiment Format:

  {
    userID: userID,
    bucket: bucketNumber, // 0-99
    app: {
      userID: userID,
      bucket: bucketNumber, // May be different
      stamp: someHash, // Used to determine when out-of-date
      features: {}, // Key,value of what is already used for this user
      dirtyFeatures: {}, // Used to override library experiments with `this.features`
    },
    shared: {} // Same format as `this.app`
  }

Added feature-client functionality

• featureClient.express is the express middleware that is added to featureClient. It attaches the req.feature() function to the req object.
• req.feature is a function that determines if a user has an experiment enabled.

Setting features via url

As of v1.0.0, you now have the ability to turn experiments on/off via the url. This is only on a per-user basis, similar to xpr-toggle.

Example [appUrl]/[path]/?xpr.featName1=true - Sets feature "featName1" to true [appUrl]/[path]/?xpr.featName1=false&featName=true - Sets feature "featName1" to false and "featName2" to true

This also allows you to enable features that normally would not show up in the list (secret features).

FAQ

1. The default read/write methods are not working.

• Make sure you are using express.cookieParser before featureClient.express. This is not done for you in case you do your own state lookups.