A lightweight A/B Testing and Feature Flag JavaScript library focused on performance ⚡️

Tesfy provides a simple but complete solution to develop A/B Tests and Feature Flags on both server and client side without relying in any storage layer. The main features of this library are:

• Lightweight and focused on performance
• Experiments
• Feature Flags
• Audience definition using jsonLogic
• Traffic Allocation
• Sticky Bucketing

Usage

Installation

npm install tesfy --save

Initialization

Import and instantiate it with a datafile. A datafile is a json that defines the experiments and features avaliable. Ideally this file should be hosted somewhere outside your application (for example in S3), so it could be fetched during boostrap or every certain time. This will allow you to make changes to the file without deploying the application.

import * as Tesfy from 'tesfy';

const datafile = {
  experiments: {
    'experiment-1': {
      id: 'experiment-1',
      percentage: 90,
      variations: [{
        id: '0',
        percentage: 50
      }, {
        id: '1',
        percentage: 50
      }]
    },
    'experiment-2': {
      id: 'experiment-2',
      percentage: 100,
      variations: [{
        id: '0',
        percentage: 100
      }],
      audience: {
        '==' : [{ var : 'countryCode' }, 'us']
      }
    }
  },
  features: {
    'feature-1': {
      id: 'feature-1',
      percentage: 50
    }
  }
};

const tesfy = new Tesfy.Engine({ datafile });

Experiments

Check which variation of an experiment is assigned to a user.

const userId = '676380e0-7793-44d6-9189-eb5868e17a86';
const experimentId = 'experiment-1';

tesfy.getVariationId(experimentId, userId); // '1'

Feature Flags

Check if a feature is enabled for a user.

const userId = '676380e0-7793-44d6-9189-eb5868e17a86';
const featureId = 'feature-1';

tesfy.isFeatureEnabled(featureId, userId); // true

Audiences

Use attributes to target an specific audience.

const userId = '676380e0-7793-44d6-9189-eb5868e17a86';
const experimentId = 'experiment-2';

tesfy.getVariationId(experimentId, userId, { countryCode: 've' }); // null
tesfy.getVariationId(experimentId, userId, { countryCode: 'us' }); // '0'

Sticky Bucketing

Optionally add a storage layer when instantiating tesfy. This layer could be whatever you want (memory cache, localStorage among others). This way even allocation or attributes change users will stick with same variation.

const tesfy = new Tesfy.Engine({
  datafile,
  storage: {
    get: (experimentId: string) => {
      return storage.get(experimentId);
    },
    store: (experimentId: string, variationId: string) => {
      return storage.save(experimentId, variationId);
    }
  }
});
const userId = '676380e0-7793-44d6-9189-eb5868e17a86';
const experimentId = 'experiment-2';

tesfy.getVariationId(experimentId, userId, { countryCode: 'us' }); // '0'
tesfy.getVariationId(experimentId, userId, { countryCode: 've' }); // '0'

Integrations

Tesfy could be integrated with several JavaScript frameworks or libraries to provide a better API to use alongside those.

• react-tesfy

Feedback

Pull requests, feature ideas and bug reports are very welcome. We highly appreciate any feedback.