ab-test-middleware

A middleware that provides an easy way to serve multiple distributions in order to run A/B/N tests.

NOTE: The middleware expects a set of production ready distributions to be built prior to using it on an app.

Usage (the TL;DR version)

Assuming your distributions are built already and available in your build folder. I suggest using navikt/ab-test/actions/build@v1 if you're running your deployments by means of GitHub Actions. The build folder should be created with the following structure:

build/
 ├── release-v1.0.0
 ├── new-design
 ├── ...
 └── login-button-placement

const express = require('express');
const { createAbTestMiddleware } = require('ab-test-middleware');

const app = express();

/**
* A function to assign a test group to an inconming request.
* @param {string} distName Distribution name sent the middleware in order 
* to know whether to assign that particular distribution to the request or not. 
* A cookie will be set in the response if the function returns a true value.  
* @returns {boolean} Boolean value that determines if the user is to be assigned 
* to the distribution's test group. 
*/
const testGroupToggleInterpreter = (distName) => {
    let enabled = false;
    // Write your logic here. Alternately make use of a feature toggle mechanism here.    
    return enabled;
}

/**
* A function that checks whether distributions are enabled and should be servable.
* @param {string} distName Distribution name sent the middleware in order to know
* whether that particular distribution is enabled or not. Disabled distributions
*  will not be served and lead to the re-assignation of a request to a different distribution.  
* @returns {boolean} Boolean value that determines if the distribution is enabled and servable. 
*/
const distributionToggleInterpreter = (distName) => {
    let enabled = false;
    // Write your logic here. Alternately make use of a feature toggle mechanism here.    
    return enabled;
}

app.use(createAbTestMiddleware({
  defaultDist: 'release-v1.0.0',            // name of the distribution (default: 'master')
  distFolder: 'build',                      // name of the distribution folder (default: 'dist') 
  cookieName: 'distributionName',           // name of the cookie to be set on test group assignation (default: 'testGroup')
  entryFile: 'landing-page.html',           // name of the entry file for your distribution (default: 'index.html')
  ingresses: ['/'],                         // array containing application ingresses (default: ['/'])
  randomizeTestGroupDistribution: true,     // whether to randomize the test group assignation (default: false)
  testGroupToggleInterpreter: testGroupToggleInterpreter,
  distributionToggleInterpreter: distributionToggleInterpreter,
}));

app.listen(3000);

Note:

If the randomizeTestGroupDistribution flag is omitted or set to false, it will result in an alphabetically ordered loop when assigning test groups to requests in the middleware. It is highly recommended to set this flag to true in cases where the testGroupToggleInterpreter does not account for randomization or does not count on a persistent distribution assignation tracking mechanism such as a feature toggle service.