Typed Env

A strongly-typed, 0-dependency environment variable parser for Typescript!

Get started

npm install --save @amccarthy1/typed-env  # npm

yarn add @amccarthy1/typed-env  # yarn

import { TypedEnv, EnumVar } from '@amccarthy1/typed-env'

const env = TypedEnv({
  ENVIRONMENT: EnumVar({ options: ['dev', 'staging', 'prod'] }),
})

doWhateverToRunApp(env.ENVIRONMENT) // env.ENVIRONMENT is of type 'dev' | 'staging' | 'prod'

Why is this useful

Many services use environment variables for runtime configuration, anything from the current environment or logging verbosity, to things like API keys and secrets. But many times, these environment variables are unvalidated and naively parsed from strings when needed.

This library aims to allow you to define environment variables in a more type-safe way. Take this example:

const environment = process.env.ENVIRONMENT

const makePayment = (amount: bigint) => {
  if (environment === 'prod') {
    makeRealPayment(amount)
  } else {
    makeMockPayment(amount)
  }
}

What if you configured your server with ENVIRONMENT=production instead of ENVIRONMENT=prod? Suddenly, all your users are getting free products because you're making mock payments instead of real ones!

If you'd used TypedEnv instead, you'd get this

const env = TypedEnv({
  ENVIRONMENT: EnumVar({ options: ['dev', 'staging', 'production'] }),
})

const makePayment = (amount: bigint) => {
  if (env.ENVIRONMENT === 'prod') {
    // TypeError!
    // `This condition will always return 'false' since
    // the types '"dev" | "staging" | "production"' and
    // '"prod"' have no overlap.`
    return makeRealPayment(amount)
  } else {
    return makeFakePayment(amount)
  }
}

What types are supported?

Currently, strings, enums, integers, booleans, and dates are supported, although you can define your own custom type using the Declaration<T> type

export type Declaration<T> = {
  variable?: string // The name of the environment variable; defaults to match the key if not specified
  parser: Parser<T> // A function (value: string) => T
}

What about optional variables?

TypedEnv is primarily built for required variables, but does support optionals using a defaultValue property. If you do not want to use an explicit default, you can use the optional() wrapper provided, which will automatically inject a default value of null and convert a Declaration<T> to a Declaration<T|null>

const env = TypedEnv({
  required: BoolVar({ defaultValue: false }),
  optional: optional(BoolVar()),
})
// This schema yields the following type object
const env: {
  required: boolean
  optional: boolean | null
}

It is generally preferred to use defaultValue over the optional wrapper, but optional may be useful in migrating existing codebases which already treat env vars as optional.