Besser

A simple & easy to use A/B testing engine for Node written in Typescript. This is the core engine which exposes API endpoints for other wrappers to integrate with. The goal of this project is to provide an isomorphic way of running A/B tests where an A/B test can be activated/triggered on server side while the goals can be captured on the client side.

Requirements

• Node >=12.7.0
• Docker

Stack

• Express as routing framework
• Typescript as programming language
• Postgres as Database
• Jest as testing framework

Download the code

First, we must download the code using git.

git clone https://github.com/jigarjain/besser.git

Setting Up Database

Before we start the project, we need to have the Postgres database up & running. For ease of development, this project ships with a docker-compose file which will setup the Postgres for you. Assuming you have the Docker installed, run the below command to setup Postgres

cd besser
docker-compose up -d

Once we the Postgres docker container (besser_postgres) running, we will create 2 database for our development. To do so, we must first connect to the above container

docker exec -it besser_postgres bash

Once we are inside the container, we can connect to the postgres by running the below command

psql -U postgres
psql (10.3 (Debian 10.3-1.pgdg90+1))
Type "help" for help.

Now that we have access to postgres, we will go ahead & create 2 databases for development & for testing respectively

postgres=# CREATE DATABASE besser;
CREATE DATABASE
postgres=# CREATE DATABASE test_besser;
CREATE DATABASE

Once done, we can exit the shell as we have successfully setup the DB.

You may also choose to skip Docker & use existing Postgres installation. In that case, you must still create the 2 databases (namely besser & test_besser) & update the .env file as mentioned in this configuration section

Installing code

As with every node project, we install the dependencies first

npm install

Setting up configuration

This project read the configuration from environment variables. The default values can be found in .env.sample file. We will create a copy of this file as .env. During bootup dotenv will read this file & sets up the values in process,env variable which will be consumed by the application.

cp .env.sample .env

Feel free to modify this configuration values in this newly created file as per your setup. If you have different database setup, you will need to update those here. Note that this file must not be checked into git. Please read the 12factor App Methodology to understand why.

Running Database Migrations

Once we have created the database & have setup the correct configuration as mentioned in previous steps, we can now proceed ahead with creating table schemas. The table schemas can be found under the folder called /migrations. We use knex as query building & migration tool in this application. To run the migration, we simply run the below command

npm run migrate-db

Compiling Typescript to JS

This application is written in Typescript. But as Node can only execute Javasript, we will first compile all the typescript files from './src' folder into ./dist by running

npm run build

Running the application

Now that we have compiled the source files into Javascript from TS, we start the node server by simply running the below command

npm serve

Development

This section will be useful if you plan to do development on this code.

NPM Scripts

First, you will need to be aware of the various build steps & their purpose. All the different build steps are orchestrated via npm scripts. Npm scripts basically allow us to call (and chain) terminal commands via npm. To call a script, simply run npm run <script-name> from the command line.

Npm Script	Description
build	Compiles all source .ts files to .js files in the dist folder
serve	Runs the server from dist as node dist/server.js which is app's entry point
start	Runs both build & serve commands
test	Runs tests using Jest test runner
test-coverage	Runs test but also collects coverage report
watch-build	Runs the build command in watch mode
watch-serve	Runs the serve command in watch mode. It uses nodemon & will restart the server if it crashes or any .js files updates
watch-ts	Runs the test command in watch mode
watch	Concurrently runs both watch-build & watch-serve. This is the command you will mostly use during development
migrate-db	Runs all the migrations from the ./migration folder'

During development, you will mostly npm run watch & npm run test

Testing

WIP

Code Style Checks

WIP

License

Licensed under the MIT License.