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

• Rewritten in TypeScript; now zero runtime dependencies
• The mode-currently-known-as-strict is now 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.
• The dotenv package is no longer shipped as part of this library. You can easily install/use it directly and pass the resulting environment object into envalid.
• The transformer option is gone, replaced by the ability to add custom middleware
• The host and ip validators are now 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 meant. You can re-implement the old behavior with a custom middleware if you wish

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 keys:
  • reporter - Pass in a function to override the default error handling and console output. See src/reporter.js for the default implementation.
  • middleware - (optional) An array of functions that can modify the env object after it's validated and cleaned. Envalid ships with default middleware, but you can customize its behavior by supplying your own

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.

const envalid = require('envalid')
const { str, email, json } = envalid

const env = envalid.cleanEnv(process.env, {
    API_KEY:            str(),
    ADMIN_EMAIL:        email({ default: 'admin@example.com' }),
    EMAIL_CONFIG_JSON:  json({ desc: 'Additional email parameters' })
})


// Read an environment variable, which is validated and cleaned during
// and/or filtering that you specified with cleanEnv().
env.ADMIN_EMAIL     // -> 'admin@example.com'

// Envalid parses 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.

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 used if the env var wasn't specified. Providing a default effectively makes the env var optional.
• 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:

const { makeValidator, cleanEnv } = require('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 }) => {
        errors.forEach(err => {
            if (err instanceof envalid.EnvError) {
                ...
            } else if (err instanceof envalid.EnvMissingError) {
                ...
            } else {
                ...
            }
        });
    }
})

Usage within React Native

Envalid can be used within React Native with a custom reporter.

react-native-config can be useful for reading env vars from a .env file.

Example:

const reactNativeConfig = require('react-native-config')
const rawConfig = reactNativeConfig.default

const validatedConfig = envalid.cleanEnv(
  rawConfig,
  {
    // validators
  },
  {
    reporter: ({ errors = {}, env = {} }) => {
      // handle errors
    },
  },
)

Utils

testOnly

A helper function called testOnly is available, in case you need an default env var 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.

Motivation

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