@scaleleap/config

Extendable configuration base class for 12 Factor application.

Install

npm i @scaleleap/config

Usage

// in ./src/config.ts

import { BaseConfig } from '@scaleleap/config'

class Config extends BaseConfig {
  public readonly TEST = this.get('TEST').asString()
}

// in ./src/app.ts

const config = new Config()

console.log(config.TEST)

Documentation

Parent Config class exposes a single protected method get, which maps to env-var#get method.

The constructor accepts a single argument, which is an dictionary of key-value strings, that represents the environment. The value defaults to process.env.

This is useful, when you'd like to override the values for testing:

const config = new Config({ NODE_ENV: '...' })

This module will automatically read .env file contents from $PWD/.env.

You can influence the discovery path of .env file via DOTENV_CONFIG_PATH environment variable.

E.g.

DOTENV_CONFIG_PATH=.env.prod node foo.js

Using a Prefix

Sometimes it is desirable to scope all of the environment variables. This can be achieved through a prefix.

Example:

class Config extends BaseConfig {
  protected readonly prefix = 'FOO_'

  public readonly TEST = this.get('TEST').asString()
}

Will then look for environment variable named FOO_TEST instead of just TEST.

Note: The underscore _ character is not included by default and must be part of your prefix.

Be careful when working with built-in variables, as they would not be discovered, because of the prefix.

Variable Expansion

It is possible to expand variables:

FOO=bar
BAZ=${FOO}-baz

When the BAZ value is expanded, the result will be:

FOO=bar
BAZ=bar-baz

Built-in Variables

There are some universal variables that are included into the config.

For now, there is just one.

`NODE_ENV`

Valid values are:

development
test
production

Example:

NODE_ENV=production node foo.js

Also comes with convenience boolean assertion getters:

isDevelopment
isTest
isProduction

Example:

const config = new Config()

if (config.isDevelopment) {
  // do something destructive
}

Guidelines

Property names should match the environment variable name, including case. E.g. NODE_ENV.
Properties should be always marked as readonly.
Use strict methods where possible, e.g. use asBoolStrict not asBool.