envalid

What is envalid?

The envalid npm package is a library for validating and accessing environment variables in Node.js applications. It helps ensure that your environment variables are present and correctly formatted, reducing the risk of runtime errors due to misconfiguration.

What are envalid's main functionalities?

Environment Variable Validation

This feature allows you to define and validate environment variables with specific types and constraints. The `cleanEnv` function ensures that the environment variables are present and correctly formatted, providing default values if necessary.

const envalid = require('envalid');
const { str, num, bool } = envalid;

const env = envalid.cleanEnv(process.env, {
  NODE_ENV: str({ choices: ['development', 'production', 'test'] }),
  PORT: num({ default: 3000 }),
  DEBUG: bool({ default: false })
});

console.log(env.NODE_ENV); // 'development', 'production', or 'test'
console.log(env.PORT); // 3000 if not specified
console.log(env.DEBUG); // false if not specified

Custom Validators

Envalid allows you to create custom validators for environment variables using the `makeValidator` function. This is useful for more complex validation logic that isn't covered by the built-in validators.

const envalid = require('envalid');
const { makeValidator } = envalid;

const myCustomValidator = makeValidator(x => {
  if (x !== 'foo' && x !== 'bar') throw new Error('Must be either foo or bar');
  return x;
});

const env = envalid.cleanEnv(process.env, {
  MY_VAR: myCustomValidator()
});

console.log(env.MY_VAR); // 'foo' or 'bar'

Type Coercion

Envalid automatically coerces environment variables to the specified types. This ensures that your application receives the correct data types, reducing the need for manual type conversion.

const envalid = require('envalid');
const { str, num, bool } = envalid;

const env = envalid.cleanEnv(process.env, {
  MY_STRING: str(),
  MY_NUMBER: num(),
  MY_BOOLEAN: bool()
});

console.log(typeof env.MY_STRING); // 'string'
console.log(typeof env.MY_NUMBER); // 'number'
console.log(typeof env.MY_BOOLEAN); // 'boolean'

Other packages similar to envalid

dotenv

Dotenv is a zero-dependency module that loads environment variables from a .env file into process.env. While it doesn't provide validation or type coercion like envalid, it is widely used for managing environment variables in Node.js applications.

joi

Joi is a powerful schema description language and data validator for JavaScript. It can be used to validate environment variables, but it requires more setup compared to envalid. Joi is more flexible and can be used for validating other types of data as well.

convict

Convict is a configuration management tool for Node.js that allows you to define a schema for your configuration, including environment variables. It provides validation and default values, similar to envalid, but also supports nested configurations and more complex use cases.

README

Envalid

Envalid is a small library for validating and accessing environment variables in Node.js (v8.12 or later) programs, aiming to:

• ensure that your program only runs when all of its environment dependencies are met
• give you executable documentation about the environment your program expects to run in
• give you an immutable API for your environment variables, so they don't change from under you while the program is running

Changes in v7.x

Version 7 is a major update, with several breaking changes. Please review the breaking changes below before upgrading:

• Rewritten in TypeScript
• Removed all runtime dependencies except for tslib
• The mode-currently-known-as-strict is removed, and its behavior is enabled by default. This means:
  • The env object will only contain the env vars that were specified by your validators.
  • Any attempt to access an invalid/missing property on the env object will cause a thrown error.
  • Any attempt to mutate the cleaned env object will cause a thrown error. You can still opt-out of strict mode by disabling the strictProxyMiddleware, but it's not recommended (see "Custom Middleware", below).
• The dotenv package is no longer shipped as part of this library. You can easily use it directly by installing it and running require('dotenv').config() before you invoke envalid's cleanEnv()
• The transformer validator option is gone, replaced by the ability to add custom middleware
• The host and ip validators are now slightly less exhaustive. If you need these to be airtight, use your own custom validator instead
• When you try to access an invalid property on the cleaned env object, the error will no longer suggest an env variable that you may have intended. You can re-implement the old behavior with a custom middleware if you wish
• NODE_ENV support is now less opinionated, and an error is no longer thrown if a value other than production/development/test is passed in. You can provide your own validator for NODE_ENV to get exactly the behavior you want. The isDev, isProduction, etc properties still work as before, and are implemented as middleware so you can override their behavior as needed.
• devDefault values are no longer used if NODE_ENV was not set in the environment (a case where Envalid otherwise assumes 'production' mode). Fixes #65

API

envalid.cleanEnv(environment, validators, options)

cleanEnv() returns a sanitized, immutable environment object, and accepts three positional arguments:

• environment - An object containing your env vars (eg. process.env)
• validators - An object that specifies the format of required vars.
• options - An (optional) object, which supports the following key:
  • reporter - Pass in a function to override the default error handling and console output. See src/reporter.ts for the default implementation.

By default, cleanEnv() will log an error message and exit (in Node) or throw (in browser) if any required env vars are missing or invalid. You can override this behavior by writing your own reporter.

import { cleanEnv, str, email, json } from 'envalid'

const env = cleanEnv(process.env, {
  API_KEY:            str(),
  ADMIN_EMAIL:        email({ default: '[e-mail]' }),
  EMAIL_CONFIG_JSON:  json({ desc: 'Additional email parameters' }),
  NODE_ENV:           str({ choices: ['development', 'test', 'production', 'staging']}),
})


// Read an environment variable, which is validated and cleaned during
// and/or filtering that you specified with cleanEnv().
env.ADMIN_EMAIL     // -> '[e-mail]'

// Envalid checks for NODE_ENV automatically, and provides the following
// shortcut (boolean) properties for checking its value:
env.isProduction    // true if NODE_ENV === 'production'
env.isTest          // true if NODE_ENV === 'test'
env.isDev           // true if NODE_ENV === 'development'

For an example you can play with, clone this repo and see the example/ directory.

git clone https://github.com/af/envalid
cd envalid
yarn prepare
node example/server.js

Validator types

Node's process.env only stores strings, but sometimes you want to retrieve other types (booleans, numbers), or validate that an env var is in a specific format (JSON, url, email address). To these ends, the following validation functions are available:

• str() - Passes string values through, will ensure an value is present unless a default value is given. Note that an empty string is considered a valid value - if this is undesirable you can easily create your own validator (see below)
• bool() - Parses env var strings "1", "0", "true", "false", "t", "f" into booleans
• num() - Parses an env var (eg. "42", "0.23", "1e5") into a Number
• email() - Ensures an env var is an email address
• host() - Ensures an env var is either a domain name or an ip address (v4 or v6)
• port() - Ensures an env var is a TCP port (1-65535)
• url() - Ensures an env var is a url with a protocol and hostname
• json() - Parses an env var with JSON.parse

Each validation function accepts an (optional) object with the following attributes:

• choices - An Array that lists the admissable parsed values for the env var.
• default - A fallback value, which will be present in the output if the env var wasn't specified. Providing a default effectively makes the env var optional. Note that default values are not passed through validation logic.
• devDefault - A fallback value to use only when NODE_ENV is not 'production'. This is handy for env vars that are required for production environments, but optional for development and testing.
• desc - A string that describes the env var.
• example - An example value for the env var.
• docs - A url that leads to more detailed documentation about the env var.

Custom validators

You can easily create your own validator functions with envalid.makeValidator(). It takes a function as its only parameter, and should either return a cleaned value, or throw if the input is unacceptable:

import { makeValidator, cleanEnv } from 'envalid'
const twochars = makeValidator(x => {
    if (/^[A-Za-z]{2}$/.test(x)) return x.toUpperCase()
    else throw new Error('Expected two letters')
})

const env = cleanEnv(process.env, {
    INITIALS: twochars()
});

Error Reporting

By default, if any required environment variables are missing or have invalid values, envalid will log a message and call process.exit(1). You can override this behavior by passing in your own function as options.reporter. For example:

const env = cleanEnv(process.env, myValidators, {
    reporter: ({ errors, env }) => {
        emailSiteAdmins('Invalid env vars: ' + Object.keys(errors))
    }
})

Additionally, envalid exposes EnvError and EnvMissingError, which can be checked in case specific error handling is desired:

const env = cleanEnv(process.env, myValidators, {
    reporter: ({ errors, env }) => {
        for (const [envVar, err] of Object.entries(errors)) {
            if (err instanceof envalid.EnvError) {
                ...
            } else if (err instanceof envalid.EnvMissingError) {
                ...
            } else {
                ...
            }
        }
    }
})

Custom Middleware (advanced)

In addition to cleanEnv(), as of v7 there is a new customCleanEnv() function, which allows you to completely replace the processing that Envalid applies after applying validations. You can use this custom escape hatch to transform the output however you wish.

envalid.customCleanEnv(environment, validators, applyMiddleware, options)

customCleanEnv() uses the same API as cleanEnv(), but with an additional applyMiddleware argument required in the third position:

• applyMiddleware - A functions that can modify the env object after it's validated and cleaned. Envalid ships (and exports) its own default middleware (see src/middleware.ts), which you can mix and match with your own custom logic to get the behavior you desire.

Utils

testOnly

A helper function called testOnly is available, in case you need an default env var value only when NODE_ENV=test. It should be used along with devDefault, for example:

const env = cleanEnv(process.env, {
  SOME_VAR: envalid.str({devDefault: testOnly('myTestValue')})
})

For more context see this issue.

Related projects

• dotenv is a very handy tool for loading env vars from .env files. It was previously used as a dependency of Envalid's. To use them together, simply call require('dotenv').config() before you pass process.env to your envalid.cleanEnv().

• react-native-config can be useful for React Native projects for reading env vars from a .env file

• fastify-envalid is a wrapper for using Envalid within Fastify

• nestjs-envalid is a wrapper for using Envalid with NestJS

Motivation

http://www.12factor.net/config