Node.jsで.envファイルを読む方法（2025年版）

Environment variables play a crucial role in application development, enabling flexible configuration without hardcoding sensitive or environment-specific details. Node.js provides multiple ways to load and manage .env files, depending on the version you are using. This article will cover methods for Node.js versions both above and below 20, as well as how to implement a custom solution if needed.

Key Takeaways

1. Node.js > 20 supports native .env file handling via CLI or process.loadEnvFile().
2. Node.js < 20 can use dotenv for .env management.
3. Custom .env file parsers offer flexibility without dependencies.

If Your Node.js Version > 20

For Node.js versions greater than 20, you can leverage built-in support to load .env files, eliminating the need for external dependencies. Here are the options:

1. Use the --env-file CLI Parameter

From Node.js v20.6.0, you can load a .env file directly using the --env-file command-line argument. This allows you to inject variables into the process.env object without modifying your code.

• Create a .env file:

  PORT=3000
  DB_HOST=localhost
  DB_USER=admin
  DB_PASSWORD=secret

• Run your application:

  node --env-file=.env app.js

  The variables defined in .env will now be available in process.env.

2. Use the process.loadEnvFile() API

From Node.js v20.12.0, the experimental process.loadEnvFile() API allows you to dynamically load a .env file within your application code.

• Example Usage:

  (async () => {
    await process.loadEnvFile('.env');
    console.log(`Server is running on port ${process.env.PORT}`);
  })();

  This method is particularly useful if you need programmatic control over when the .env file is loaded. However, since it is an experimental feature, its behavior may change in future Node.js releases.

If Your Node.js Version < 20

For earlier versions of Node.js, you will need to use external libraries or implement your own logic to handle .env files.

1. Use the dotenv Library

The dotenv library is a widely used solution for managing .env files. It works seamlessly across all Node.js versions and is simple to set up.

• Install the library:

  npm install dotenv

• Use it in your application:

  require('dotenv').config();
  
  console.log(`Server is running on port ${process.env.PORT}`);

  The .env file is automatically loaded, and its variables are added to process.env.

2. Implement Your Own Logic

If you prefer not to use external libraries, you can write a simple function to parse .env files and load them into process.env.

• Example Implementation:

  const fs = require('fs');
  const path = require('path');
  
  function loadEnvFile(filePath) {
    try {
      const resolvedPath = path.resolve(filePath);
      const data = fs.readFileSync(resolvedPath, 'utf-8');
  
      data.split(/\r?\n/).forEach((line) => {
        const trimmedLine = line.trim();
        if (!trimmedLine || trimmedLine.startsWith('#')) return;
  
        const [key, value] = trimmedLine.split('=');
        if (key && value !== undefined) {
          process.env[key.trim()] = value.trim();
        }
      });
  
      console.log('Environment variables loaded successfully.');
    } catch (error) {
      console.error(`Error loading .env file: ${error.message}`);
    }
  }
  
  // Usage
  loadEnvFile('.env');
  console.log(`Server is running on port ${process.env.PORT}`);

  This approach provides full control over how .env files are parsed and processed, which can be useful for advanced use cases or custom formats.

FAQs

What is the advantage of --env-file over dotenv?

It eliminates the need for third-party libraries.

Is process.loadEnvFile() stable for production?

No, it’s an experimental feature in Node.js v20.12.0+.

Can I use these methods with custom .env formats?

Only a custom parser allows full control over formats.

Conclusion

Depending on your Node.js version, you can choose the most suitable approach to manage .env files:

1. Node.js > 20:
   • Use the --env-file CLI parameter for quick loading.
   • Use the process.loadEnvFile() API for dynamic programmatic control.
2. Node.js < 20:
   • Use the popular dotenv library for reliable and easy-to-use support.
   • Implement your own .env loader for custom requirements.

Each method has its benefits, and choosing the right one depends on your project needs and Node.js version.

---

We are Leapcell, your top choice for deploying Node.js projects to the cloud.

Leapcell is the Next-Gen Serverless Platform for Web Hosting, Async Tasks, and Redis:

Multi-Language Support

• Develop with Node.js, Python, Go, or Rust.

Deploy unlimited projects for free

• pay only for usage — no requests, no charges.

Unbeatable Cost Efficiency

• Pay-as-you-go with no idle charges.
• Example: $25 supports 6.94M requests at a 60ms average response time.

Streamlined Developer Experience

• Intuitive UI for effortless setup.
• Fully automated CI/CD pipelines and GitOps integration.
• Real-time metrics and logging for actionable insights.

Effortless Scalability and High Performance

• Auto-scaling to handle high concurrency with ease.
• Zero operational overhead — just focus on building.

Explore more in the Documentation!

Follow us on X: @LeapcellHQ