trust-env

Validate process.env variables against a contract for safer use.

Fails at runtime if contract requirements are not met.

Installation

yarn add trust-env

Usage

// src/env.ts

import dotenv from 'dotenv';
import TrustEnv from 'trust-env';

// Or whatever the way env variables are injected in Node process
dotenv.config();

// Contract for declaring and validating variables to be used
export default TrustEnv([
  {
    key: 'MYSQL_HOST',
    type: 'string',
  },
  {
    key: 'MYSQL_PORT',
    // Cast process.env.MYSQL_PORT into number
    type: 'number',
  },
  {
    key: 'MYSQL_SSL',
    type: 'string',
    // Allow process.env.MYSQL_SSL to be not found in process.env
    // env.MYSQL_SSL returns undefined
    required: false,
  },
  {
    key: 'MYSQL_PASSWORD',
    type: 'string',
    // Allow process.env.MYSQL_PASSWORD to be not found in process.env
    required: false,
    // env.MYSQL_PASSWORD returns 'root'
    preset: 'root',
  },
  {
    key: 'DEFAULT_USER',
    type: 'json',
    validator: ({ value, isJs }) => isJs.propertyDefined(value, 'name'),
  },
]);

// src/index.ts

import './env';

// ...

// src/anywhere.ts

import env from './env';

// Access to variables
const { MYSQL_PORT } = env;
const DEFAULT_USER = env.get('DEFAULT_USER');
const MYSQL_VARIABLES = env.getPrefix('MYSQL');

// ...

Make the following "top of file" validations deprecated:

// src/function.ts

assert(process.env.MYSQL_HOST, Error, 'Missing env var [MYSQL_HOST]');

// ...

Typing

// src/env.ts

import dotenv from 'dotenv';
import TrustEnv from 'trust-env';

dotenv.config();

type Env = {
  BASE_API_URL: string;
  APPLICATION_KEY: string;
};

/* pass your type as a generic */
export default TrustEnv<Env>([
  { key: 'BASE_API_URL', type: 'string' },
  { key: 'APPLICATION_KEY', type: 'string' },
]);

// src/anywhere.ts

import env from '@env';

interface Environment {
  BASE_API_URL: string;
}

export const myMethod = (environment: Environment = env) => {
  console.log(environment.BASE_API_URL);
};

Features

Caches process.env variables to work only with it (if process.env is updated, changes will have no effect)

An entry in the contract:

• key: name of the variable to look for in process.env
• type:
  • cast the actual process.env variable
  • supported:
    • boolean
    • date
    • integer
    • integersArray
    • json
    • number
    • numbersArray
    • string
    • stringsArray
• required: (optional, default: true) process.env variable is not found
• preset: (optional) used when process.env variable is not found and is not required. Is cast.
• transform: (optional) function to transform the cast variable
• validator: (optional) function to validate the cast and transformed variable

Transform

• Params:
  • value: the cast process.env value
  • entry: the current entry to be validated
  • contract: the whole contract
  • isJs library

Validator

• Returns a boolean to validate the process.env value
• Params:
  • value: the cast and transformed process.env value
  • entry: the current entry to be validated
  • contract: the whole contract
  • isJs library

TrustEnv([
  {
    key: 'MYSQL_HOST',
    type: 'string',
    validator: ({ value }) => value.startsWith('__'),
  },
]);