envvar

envvar is a tiny JavaScript package for deriving JavaScript values from environment variables.

const envvar = require('envvar');
 
const GITHUB_API_TOKEN = envvar.string('GITHUB_API_TOKEN');
const HTTP_MAX_SOCKETS = envvar.number('HTTP_MAX_SOCKETS');
const ENABLE_FEATURE_X = envvar.boolean('ENABLE_FEATURE_X', false);

If one argument is provided the environment variable is required. If the environment variable is not set, an envvar.UnsetVariableError is thrown:

UnsetVariableError: No environment variable named "GITHUB_API_TOKEN"

If two arguments are provided the environment variable is optional. If the environment variable is not set, the default value is used. The default value must be of type Boolean in the case of envvar.boolean, of type Number in the case of envvar.number, or of type String in the case of envvar.string. If it is not, a TypeError is thrown.

The value of the environment variable must be the string representation of a value of the appropriate type: for envvar.boolean the only valid strings are 'true' and 'false'; for envvar.number applying Number to the string must not produce NaN. If the environment variable is set but does not have a suitable value, an envvar.ValueError is thrown:

ValueError: Value of process.env["HTTP_MAX_SOCKETS"] does not represent a number

envvar.oneOf

This is similar to envvar.string, but with constraints. There may be a small number of valid values for a given environment variable. For example:

const NODE_ENV = envvar.oneOf('NODE_ENV', ['development', 'staging', 'production']);

This states that process.env.NODE_ENV must be set to development, staging, or production.

A default value may be provided:

const NODE_ENV = envvar.oneOf('NODE_ENV', ['development', 'staging', 'production'], 'production');

This states that process.env.NODE_ENV must either be unset (in which case the default value is assumed), or set to development, staging, or production.