auto-config 🛠✨

Intro

A Unified Config & Arguments Library for Node.js!

Featuring support for environment variables, command line arguments, and (soon) JSON/YAML/INI files!

Why

There are so many config libraries, do we really need another??? Well, possibly!

No existing library I tried met my requirements.

My goals & requirements include:

• Enable dynamic app config. See '12 Factor App' on Config
• TypeScript support.
• Portable pattern (not filesystem-locked, browser support.)
• Simple, memorable & terse config format.

Table of Contents

• auto-config 🛠✨
  • Intro
  • Why
  • Install
  • Example: AWS Access Config
  • Example: Web App with Database Config
  • Example: Linux Move Command Arguments
  • Example: Feature Flags
  • Example: Runtime Usage Behavior
    • Command line arguments
    • Mix of environment and command arguments
    • Single-letter flag arguments
    • Error on required fields
    • CLI Help Output
  • TODO
    • Add Shorthand Object Support
  • Credit and References

Install

npm install @elite-libs/auto-config

yarn add @elite-libs/auto-config

Example: AWS Access Config

// `./src/aws-config.ts`
import { autoConfig } from '@elite-libs/auto-config';
import AWS from 'aws-sdk';

const awsConfig = getAwsConfig();

AWS.config.update({
  ...awsConfig,
  endpointDiscoveryEnabled: true,
});

function getAwsConfig() {
  return autoConfig({
    region: {
      help: 'AWS Region',
      args: ['--region', '-r', 'AWS_REGION'],
      default: 'us-west-1',
      required: true,
    },
    accessKeyId: {
      help: 'AWS Access Key ID',
      args: ['--access-key-id', 'AWS_ACCESS_KEY_ID'],
      required: true,
    },
    secretAccessKey: {
      help: 'AWS Secret Access Key',
      args: ['--secret-access-key', 'AWS_SECRET_ACCESS_KEY'],
      required: true,
    },
  });
}

Example: Web App with Database Config

// `./src/config.ts`
import { autoConfig } from '@elite-libs/auto-config';

export default autoConfig({
  databaseUrl: {
    help: 'The Postgres connection string.',
    args: ['--databaseUrl', '--db', 'DATABASE_URL'],
    required: true,
  },
  port: {
    help: 'The port to start server on.',
    args: ['--port', '-p', 'PORT'],
    type: 'number',
    required: true,
  },
  debugMode: {
    help: 'Debug mode.',
    args: ['--debug', '-D'],
    type: 'boolean',
    default: false,
  },
});

// `./src/server.js`
import express from 'express';
import catRouter from './routes/cat';
import config from './config';

const { port, debugMode } = config;

const logMode = debugMode ? "dev" : "combined";

export const app = express()
  .use(express.json())
  .use(express.urlencoded({ extended: false }))
  .use(morgan(logMode))
  .get('/', (req, res) => res.send('Welcome to my API'))
  .use('/cat', catRouter);

app.listen(port)
  .on('error', console.error)
  .on('listening', () =>
    console.log(`Started server: http://0.0.0.0:${port}`);
  );

Example: Linux Move Command Arguments

const moveOptions = autoConfig({
  force: {
    args: '-f',
    help: 'Do not prompt for confirmation before overwriting the destination path.  (The -f option overrides any previous -i or -n options.)'
    type: 'boolean',
  },
  interactive: {
    args: '-i',
    help: 'Cause mv to write a prompt to standard error before moving a file that would overwrite an existing file.  If the response from the standard input begins with the character `y` or `Y`, the move is attempted.  (The -i option overrides any previous -f or -n options.)'
    type: 'boolean',
  },
  noOverwrite: {
    args: '-n',
    help: 'Do not overwrite an existing file.  (The -n option overrides any previous -f or -i options.)',
    type: 'boolean',
  },
  verbose: {
    args: '-v',
    help: 'Cause mv to be verbose, showing files after they are moved.',
    type: 'boolean',
  }
});

Example: Feature Flags

// `./src/config/featureFlags.ts`
export const Flags = autoConfig({
  dashboard: {
    args: ['FEATURE_FLAG_DASHBOARD'],
    type: 'enum',
    enum: ['off', 'variant1'],
    default: 'off',
  },
  checkout: {
    args: ['FEATURE_FLAG_CHECKOUT'],
    type: 'enum',
    enum: ['off', 'variant1', 'variant2'],
    default: 'off',
  },
  register: {
    args: ['FEATURE_FLAG_REGISTER'],
    type: 'enum',
    enum: ['off', 'variant1', 'variant2', 'variant3', 'variant4'],
    default: 'off',
  },
});

Example: Runtime Usage Behavior

Command line arguments

node ./src/app.js \
  --port 8080 \
  --databaseUrl 'postgres://localhost/postgres' \
  --debug
# { port: 8080, databaseUrl: 'postgres://localhost/postgres', debug: true }

Mix of environment and command arguments

DATABASE_URL=postgres://localhost/postgres \
  node ./src/app.js \
    --port 8080 \
    --debug
# { port: 8080, databaseUrl: 'postgres://localhost/postgres', debug: true }

Single-letter flag arguments

node ./src/app.js \
  -D \
  --port 8080 \
  --databaseUrl 'postgres://localhost/postgres'
# { port: 8080, databaseUrl: 'postgres://localhost/postgres', debug: true }

Error on required fields

node ./src/app.js \
  --port 8080
# Error: databaseUrl is required.

CLI Help Output

node ./src/app.js --help

╭───────────────────────────┬────────────────────────────────────────────┬──────────────────────────────────────────────────────────╮
│                           │                                            │                                                          │
│  Name                     │  Help                                      │  CLI Args, Env Name(s)                                   │
│                           │                                            │                                                          │
├───────────────────────────┼────────────────────────────────────────────┼──────────────────────────────────────────────────────────┤
│databaseUrl*               │The Postgres connection string.             │--databaseUrl, DATABASE_URI, DATABASE_URL                 │
├───────────────────────────┼────────────────────────────────────────────┼──────────────────────────────────────────────────────────┤
│port*                      │The port to serve content from.             │-p, --port                                                │
├───────────────────────────┼────────────────────────────────────────────┼──────────────────────────────────────────────────────────┤
│[debugMode] = false        │Debug mode.                                 │-D, --debug                                               │
├───────────────────────────┼────────────────────────────────────────────┼──────────────────────────────────────────────────────────┤
│help                       │Show this help.                             │--help                                                    │
├───────────────────────────┼────────────────────────────────────────────┼──────────────────────────────────────────────────────────┤
│version                    │Show the current version.                   │--version                                                 │
╰───────────────────────────┴────────────────────────────────────────────┴──────────────────────────────────────────────────────────╯

TODO

Add Shorthand Object Support

export const config = autoConfig({
  "databaseUrl": ['--databaseUrl', '--db', 'DATABASE_URL'],
  "port": ['--port', '-p', 'PORT'],
  "debug": ['--debug', '-D'],
});

• Add browser bundler support by allowing args like this: () => process.env.FEAT_FLAG_V1. To support non-dynamic env references.
• Auto --help output.
  • Add support to define free-text in help output. E.g. See sections from "man pages" - often labelled like DESCRIPTION, Usage, etc.
• Add support for loading stringified JSON.
• Add option to include the _ or __ args from minimist. (Overflow/unparsed extra args.)
• Enum support.
• Inverting boolean flags with --no-debug versus --debug.
• Plugin modules with minimal overhead. (e.g. 3rd party loaders: AWS SSM, AppConfig, Firebase Config, etc.)
  • Example args: {ssm:/app/flags/path/admin_dashboard}
    • ['{ssm:/app/flags/path/admin_dashboard}', 'FLAG_ADMIN_DASHBOARD_ENABLED', '--flagAdminDashboard', '--flag-admin-dashboard']
• Support for loading files, and structured data with dotted key paths.
  • Example args: {config.flags.admin_dashboard}
    • ['{config.flags.admin_dashboard}', 'FLAG_ADMIN_DASHBOARD_ENABLED', '--flagAdminDashboard', '--flag-admin-dashboard']
• --version output.
• default values.
• required values.
• Zod validators for optional, min, max, gt, gte, lt, lte.

Credit and References

Projects researched, with any notes on why it wasn't a good fit.

• yargs - like the fluent API, and command syntax. Could use as base library. Env vars could be handled via default helper function to check for env keys. Or we could transform yargs config into overlapping format.
• commander - like the many ways to configure arguments. Could probably be used as underlying library, however initial attempt was slower than starting from scratch.
• cosmiconfig - focused too much on disk-backed config.
• rc - focused on 'magically' locating disk-backed config.
• node-convict - great pattern, but limited TypeScript support.
• nconf - setter & getter, plus the hierarchy adds extra layers.
• conf - too opinionated (writing to disk.) Interesting use of JSON Schemas, Versioning, and Migrations.
• gluegun - great design, focused on opinionated design of CLI apps though.
• configstore - replaced by conf.