Node.js, the difference between development and production

There is no difference between development and production in Node.js, i.e., there are no specific settings you need to apply to make Node.js work in a production configuration. However, a few libraries in the npm registry recognize using the NODE_ENV variable and default it to a development setting. Always run your Node.js with the NODE_ENV=production set.

A popular way of configuring your application is by using the twelve factor methodology.

NODE_ENV in Express

In the wildly popular express framework, setting the NODE_ENV to production generally ensures that:

• logging is kept to a minimum, essential level
• more caching levels take place to optimize performance

This is usually done by executing the command

export NODE_ENV=production

in the shell, but it's better to put it in your shell configuration file (e.g. .bash_profile with the Bash shell) because otherwise the setting does not persist in case of a system restart.

You can also apply the environment variable by prepending it to your application initialization command:

NODE_ENV=production node app.js

For example, in an Express app, you can use this to set different error handlers per environment:

if (process.env.NODE_ENV === 'development') {
  app.use(express.errorHandler({ dumpExceptions: true, showStack: true }));
}
if (process.env.NODE_ENV === 'production') {
  app.use(express.errorHandler());
}

For example [Pug](https://pugjs.org], the templating library used by [Express.js](https://expressjs.com], compiles in debug mode if NODE_ENV is not set to production. Express views are compiled in every request in development mode, while in production they are cached. There are many more examples.

This environment variable is a convention widely used in external libraries, but not within Node.js itself.

Why is NODE_ENV considered an antipattern?

An environment is a digital platform or a system where engineers can build, test, deploy, and manage software products. Conventionally, there are four stages or types of environments where our application is run:

• Development
• Staging
• Production
• Testing

The fundamental problem of NODE_ENV stems from developers combining optimizations and software behavior with the environment their software is running on. The result is code like the following:

if (process.env.NODE_ENV === 'development') {
  // ...
}
if (process.env.NODE_ENV === 'staging') {
  // ...
}
if (process.env.NODE_ENV === 'production') {
  // ...
}
if (process.env.NODE_ENV === 'testing') {
  // ...
}

While this might look harmless, it makes the production and staging environments different, thus making reliable testing impossible. For example a test and thus a functionality of your product could pass when NODE_ENV is set to development but fail when setting NODE_ENV to production. Therefore, setting NODE_ENV to anything but production is considered an antipattern.