Xpr-express NPM

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    stamp: someHash, // Used to determine when out-of-date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).