Env Core

env-core is a lightweight, type-safe environment variable validation library for Node.js projects.

Features

• Type-safe environment variable validation
• Supports String, Number, and Boolean types
• Optional variables with default values
• Detailed error messages for validation failures
• Compatible with Express.js, NestJS, and other Node.js frameworks
• Minimal dependencies
• Works with both ESM (import) and CommonJS (require)

Installation

Install env-core package:

npm install env-core

Usage

Define the Environment Schema

First, define a schema for your environment variables. Here are three different use cases for how you can set up your envSchema:

Use Case 1: Simple Types

Environment variables are defined using simple types without additional options.

// src/envSchema.js

export const envSchema = {
  PORT: Number,
  NODE_ENV: String,
  DEBUG: Boolean,
  HOST: String,
};

Use Case 2: Configuration Options

You can include default values and exclude requirement check for specific environment variables.

// src/envSchema.js

export const envSchema = {
  DEBUG: { 
    type: Boolean,
    default: false,
  },
  HOST: {
    type: String,
    default: '0.0.0.0',
    required: false,
  },
};

Use Case 3: Mixed Configuration

You use a mix of simple types and configuration options for both flexibility and control.

// src/envSchema.js

export const envSchema = {
  PORT: Number,
  NODE_ENV: String,
  DEBUG: {
    type: Boolean,
    default: false,
  },
  HOST: {
    type: String,
    default: '0.0.0.0',
    required: false,
  },
};

EnvSchema Format

The envSchema object defines the structure and validation rules for your environment variables. Each key in the object represents an environment variable, and the value defines its type and optional settings.

Format	Description	Example
KEY: Type	Simple type definition (required by default)	PORT: Number
KEY: { type: Type, default: value }	Type with default value (optional)	DEBUG: { type: Boolean, default: false }
KEY: { type: Type, required: boolean }	Explicitly set if required	NODE_ENV: { type: String, required: false }

Supported types: String, Number, Boolean

Usage Examples

Express.js

Call the validateEnv function with your schema to validate the environment variables before starting your server.

// src/index.js

import express from 'express';
import { validateEnv } from 'env-core';
import { envSchema } from './envSchema.js'; // Import the validation schema

// Validate the environment variables using the schema
const env = validateEnv(envSchema); // Option 1: Validates using environment variables or defaults to .env
// const env = validateEnv(envSchema, 'test.env'); // Option 2: Validates using a custom env file

const app = express();

app.get('/', (req, res) => {
    res.send('Hello World!');
});

app.listen(env.PORT, () => {
    console.log(`Server is running on port ${env.PORT}`);
});

If any environment variable is missing or has the wrong type, the app will not start, and a detailed error message will be displayed.

NestJS

env-core can be integrated into a NestJS project to validate environment variables during the module initialization process.

// src/app.module.ts

import { Module } from '@nestjs/common';
import { ConfigModule } from '@nestjs/config';
import { validateEnv } from 'env-core';
import { envSchema } from './envSchema.js'; // Import the validation schema

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      validate: (config) => validateEnv(envSchema, config), // Validate environment variables
    }),
  ],
  controllers: [],
  providers: [],
})
export class AppModule {}

If the validation fails, NestJS will not initialize, and a descriptive error message will be printed.

API Reference

validateEnv(schema: EnvSchema, envPath?: string)

• schema: An object that defines the required environment variables and their types. Supported types are String, Number, and Boolean.
• envPath (optional): A string specifying a custom .env file to load (e.g., 'test.env').

Returns

A function that takes the envConfig (defaults to process.env) and validates it against the schema. If validation passes, the function returns the validated config. If validation fails, an error is thrown.

Error Handling

If validation fails, the package throws an error with detailed information, including:

• Missing required environment variables
• Environment variables with incorrect types

Example Error Message:

Environment validation failed:
- Missing required field: NODE_ENV
- Missing required field: DEBUG
- DEBUG should be a boolean

Example of .env or custom env file

PORT=3000
NODE_ENV=development
DEBUG=true

Contributing

Feel free to submit issues or pull requests if you find bugs or have ideas for improvements.

License

This package is licensed under the MIT License.