@arpinum/config

One man's constant is another man's variable.
(Alan Perlis)

@arpinum/config is a simple module to read configuration from env variables.

It helps you implement a 12-factor configuration.

Installation

npm install @arpinum/config --save

Usage

Given those env variables:

export DATABASE_URL=mongodb://localhost:27017/database
export LOG_LEVEL=info

In your app, require the module then read the configuration:

const { loadConfiguration } = require("@arpinum/config");

const configuration = loadConfiguration({
  databaseUrl: {
    env: "DATABASE_URL",
  },
  logLevel: {
    env: "LOG_LEVEL",
  },
});

console.log(configuration);

The output is:

{
  databaseUrl: 'mongodb://localhost:27017/database',
  logLevel: 'info'
}

Nested configuration

Configuration can be nested:

const configuration = loadConfiguration({
  database: {
    url: {
      env: "DATABASE_URL",
    },
    user: {
      env: "DATABASE_USER",
    },
  },
});

console.log(configuration);

The output is:

{
  database: {
    url: the_url,
    user: the_user
  }
}

Default value

A default value can be used if the variable is missing:

const configuration = loadConfiguration({
  logLevel: {
    env: "LOG_LEVEL",
    default: "info",
  },
});

This is particularly useful for development environment.

Overriding defaults

Though default values can be described in schema, it may be useful to override them if you load configuration from another source.

const configuration = loadConfiguration(
  {
    log: {
      level: {
        env: "LOG_LEVEL",
      },
    },
  },
  {
    defaults: {
      log: { level: "debug" },
    },
  },
);

Fallback variables

More than one variable can be provided for a key. The first defined value will be used.

Example:

const configuration = loadConfiguration({
  port: {
    env: ["PORT", "DB_PORT", "PG_PORT"],
  },
});

This is usefull when variables change between deployment environments.

Required value

If a property is marked as required, the module will throw an error if the corresponding variable is missing.

Example:

const configuration = loadConfiguration({
  logLevel: {
    env: "LOG_LEVEL",
    required: true,
  },
});

Type conversion

A property can be cast to a given type, provided representation is compatible.

Example:

const configuration = loadConfiguration({
  retryCount: {
    env: "RETRY_COUNT",
    type: "integer",
  },
});

Available types:

• string (default),
• integer,
• boolean,
• float

Boolean representations (case insensitive):

• true: true, yes
• false: false, no

Custom type conversion

A property can be converted using a custom conversion function.

Example:

const configuration = loadConfiguration({
  timeoutInMilliseconds: {
    env: "TIMEOUT_IN_SECONDS",
    convert: (v) => v * 1000,
  },
});

Inspiration

My main source of inspiration is 12factor-config, a simple module made by chilts.

I thank him for his work, his module helped me a while.

License

MIT