⚙️ Configer

Production-grade config loader with cosmiconfig-level capabilities and a clean original API

💡 Highlights

• 🎯 Deterministic config resolution with 4 search strategies (none, project, workspace, global) and 40+ default search places per module name
• 📦 First-class support for 10+ formats — JSON, YAML, TOML, JSON5, JSONC, .env, JS/TS modules, and package.json properties — with both async and sync loaders
• 🔗 Config inheritance ($import/extends), environment overlays ($env/$development), schema validation, and plugin hooks — all built-in with zero config
• 🏗️ Clean Architecture internals with full DI container, making every component testable, replaceable, and independently extensible

📚 Table of Contents

• Description
• Tech Stack
• Features
• Architecture
• Project Structure
• Prerequisites
• Installation
• Usage
• Roadmap
• FAQ
• License
• Acknowledgments

📖 Description

Configer is a typed, extensible configuration loader for Node.js that resolves config files across project, workspace, and global scopes — with deterministic search plans, config inheritance chains, environment overlays, schema validation, and plugin lifecycle hooks.

Built with clean architecture principles (domain → application → infrastructure → presentation layers) and powered by a dependency injection container, Configer delivers the flexibility of cosmiconfig with stronger type safety, explicit error codes, and a modular internal design.

Real-World Use Cases

• CLI Tools & Dev Tooling: Automatically discover .toolrc, .toolrc.yaml, tool.config.ts, or package.json properties — just like ESLint, Prettier, and Babel do — but with full TypeScript generics and schema validation out of the box.
• Monorepo Configuration: Use the workspace search strategy to traverse from any nested package up to the workspace root, merging shared base configs with per-package overrides.
• Multi-Environment Apps: Define $development, $production, or $env blocks directly in config files. Configer strips inactive environments and deep-merges the active one — no extra tooling required.
• Plugin Ecosystems: Extend the config lifecycle with beforeFind, afterRead, and onError hooks to inject defaults, validate against external schemas, or log diagnostics.
• Library Authors: Ship a typed config contract (IConfigOptions<TEntity>) so consumers get autocomplete and compile-time safety for your tool's configuration.

🛠️ Tech Stack

🚀 Features

• ✨ **Async & Sync Clients — createConfiger() for async IO with watch support; createConfigerSync() for synchronous-only flows with strict fail-fast guarantees**
• ✨ **10+ Built-in Loaders — JSON, JSON5, JSONC, YAML, TOML, .env, JS (.js/.cjs/.mjs), TypeScript (.ts/.cts/.mts), and package.json property extraction**
• ✨ **4 Search Strategies — none (current directory), project (up to package.json), workspace (up to monorepo root), global (including XDG config home)**
• ✨ **Config Inheritance — Merge parent configs via extends or $import directives with circular reference detection and source chain tracking**
• ✨ **Environment Overlays — $development, $production, or $env map blocks are deep-merged for the active environment and stripped from output**
• ✨ **Built-in Schema Validation — Declare required fields, types, defaults, nested objects, array items, and custom validators without external dependencies**
• ✨ **Plugin Lifecycle Hooks — beforeFind, afterFind, beforeRead, afterRead, and onError hooks for extending every stage of config resolution**
• ✨ **Custom Loaders — Register async/sync loaders for any file extension (.ini, .xml, .custom) via the loaders option**
• ✨ **Watch Mode — File system watcher with debounced refresh, automatic cache invalidation, and clean IWatchHandle.close() cleanup**
• ✨ **Caching Layer — Separate find/read caches with granular clearFindCache(), clearReadCache(), and clearCaches() controls**
• ✨ **Stable Error Codes — Every failure throws ConfigError with a machine-readable CODE and human-readable SUGGESTIONS array**
• ✨ **Clean Architecture — Domain-driven layers (domain → application → infrastructure → presentation) with full DI container for testability**

🏗 Architecture

System Architecture

flowchart TD
    presentation[Presentation Layer]
    application[Application Layer]
    domain[Domain Layer]
    infrastructure[Infrastructure Layer]
    presentation --> application
    presentation --> infrastructure
    application --> domain
    infrastructure --> application
    infrastructure --> domain
    subgraph presentation
        createConfiger[createConfiger]
        createConfigerSync[createConfigerSync]
    end
    subgraph infrastructure
        diContainer[DI Container]
        loaderRegistry[Loader Registry]
        searchResolvers[Search Resolvers]
        cacheAdapter[Memory Cache]
        schemaValidator[Schema Validator]
        deepMerge[Deep Merge]
        fileWatcher[File Watcher]
    end
    subgraph application
        resolveSearchPlan[ResolveSearchPlanUseCase]
    end
    subgraph domain
        configClient[IConfigClient]
        configResult[IConfigResult]
        configError[ConfigError]
        pluginContract[IConfigPlugin]
    end

Data Flow

sequenceDiagram
    participant User
    participant Client as ConfigClient
    participant Plugins as Plugin Hooks
    participant SearchPlan as ResolveSearchPlan
    participant Cache as MemoryCache
    participant Loader as LoaderRegistry
    participant Merge as DeepMerge
    participant Schema as SchemaValidator
    User->>Client: findConfig(searchFrom?)
    Client->>Plugins: beforeFind(context)
    Client->>Cache: getFindResult(key)
    alt Cache Hit
        Cache-->>Client: cached result
    else Cache Miss
        Client->>SearchPlan: execute(options)
        SearchPlan-->>Client: candidateFilepaths[]
        loop Each candidate
            Client->>Loader: load(filepath, content)
            Loader-->>Client: raw config
            Client->>Merge: resolveInheritance(extends/$import)
            Merge-->>Client: merged config
            Client->>Client: resolveEnvironmentOverrides($env)
            Client->>Schema: validate(config, descriptor)
            Schema-->>Client: validated config
        end
        Client->>Cache: setFindResult(key, result)
    end
    Client->>Plugins: afterFind(result, context)
    Client-->>User: IConfigResult or null

📁 Project Structure

Configer/
├── docs/
│   ├── api-reference/
│   │   ├── error-codes/
│   │   ├── factories/
│   │   ├── interfaces/
│   │   ├── types/
│   │   ├── _meta.js
│   │   └── page.mdx
│   ├── core-concepts/
│   │   ├── caching-and-watch/
│   │   ├── environment-overrides/
│   │   ├── inheritance-and-merge/
│   │   ├── resolution-flow/
│   │   ├── schema-validation/
│   │   ├── _meta.js
│   │   └── page.mdx
│   ├── getting-started/
│   │   ├── first-client/
│   │   ├── first-config-read/
│   │   ├── installation/
│   │   ├── sync-mode/
│   │   ├── _meta.js
│   │   └── page.mdx
│   ├── guides/
│   │   ├── custom-loaders/
│   │   ├── custom-search-places/
│   │   ├── package-json-property/
│   │   ├── plugins/
│   │   ├── watch-mode/
│   │   ├── _meta.js
│   │   └── page.mdx
│   ├── _meta.js
│   └── page.mdx
├── examples/
│   ├── 01-basic-usage/
│   │   └── main.ts
│   ├── 02-search-strategies/
│   │   └── main.ts
│   ├── 03-file-formats/
│   │   └── main.ts
│   ├── 04-inheritance/
│   │   └── main.ts
│   ├── 05-environment-overrides/
│   │   └── main.ts
│   ├── 06-plugins/
│   │   └── main.ts
│   ├── 07-schema-validation/
│   │   └── main.ts
│   ├── 08-custom-loaders/
│   │   └── main.ts
│   ├── 09-watch-mode/
│   │   └── main.ts
│   ├── 10-package-json-property/
│   │   └── main.ts
│   ├── README.md
│   └── tsconfig.json
├── scripts/
│   ├── clean.function.js
│   └── validate-documentation.function.js
├── src/
│   ├── application/
│   │   ├── dto/
│   │   ├── interface/
│   │   ├── use-case/
│   │   └── index.ts
│   ├── domain/
│   │   ├── entity/
│   │   ├── error/
│   │   ├── type/
│   │   └── index.ts
│   ├── infrastructure/
│   │   ├── adapter/
│   │   ├── cache/
│   │   ├── di/
│   │   ├── loader/
│   │   ├── resolver/
│   │   ├── service/
│   │   ├── watcher/
│   │   └── index.ts
│   ├── presentation/
│   │   ├── function/
│   │   └── index.ts
│   └── index.ts
├── test/
│   ├── e2e/
│   │   ├── configer-error-paths.end-to-end.test.ts
│   │   └── configer-integration.end-to-end.test.ts
│   └── unit/
│       ├── application/
│       ├── domain/
│       ├── infrastructure/
│       └── presentation/
├── commitlint.config.js
├── eslint.config.js
├── generated-logo.png
├── lint-staged.config.js
├── package-lock.json
├── package.json
├── prettier.config.js
├── README.md
├── release.config.js
├── rollup.config.js
├── tsconfig.build.json
├── tsconfig.json
├── vitest.config.js
├── vitest.end-to-end.config.js
└── vitest.unit.config.js

📋 Prerequisites

• Node.js >= 20.0.0
• npm >= 9.0.0 (or pnpm / yarn equivalent)
• ESM-compatible project ("type": "module" in package.json)

🛠 Installation

# Using npm
npm install @elsikora/configer

# Using pnpm
pnpm add @elsikora/configer

# Using yarn
yarn add @elsikora/configer


Verify the installation:

ts
import { createConfiger } from '@elsikora/configer';

const client = createConfiger({ moduleName: 'my-app' });
console.log(typeof client.findConfig === 'function'); // true

💡 Usage

Basic Async Usage

import { createConfiger } from '@elsikora/configer';
import type { IConfigClient, IConfigResult } from '@elsikora/configer';

type AppConfig = {
  serviceName: string;
  isFeatureEnabled: boolean;
};

const client: IConfigClient<AppConfig> = createConfiger<AppConfig>({
  moduleName: 'my-app',
  cwd: process.cwd(),
});

const result: IConfigResult<AppConfig> | null = await client.findConfig();

if (result) {
  console.log(result.filepath); // /project/.my-apprc.json
  console.log(result.config?.serviceName); // "billing-api"
}

Sync Mode

import { createConfigerSync } from '@elsikora/configer';

const client = createConfigerSync<{ retries: number }>({
  moduleName: 'my-app',
});

const result = client.findConfig();
console.log(result?.config?.retries); // 3

Search Strategies

// Search only the current directory
const client = createConfiger({ moduleName: 'app', searchStrategy: 'none' });

// Ascend until nearest package.json
const client = createConfiger({ moduleName: 'app', searchStrategy: 'project' });

// Ascend until workspace root (.git, pnpm-workspace.yaml, etc.)
const client = createConfiger({ moduleName: 'app', searchStrategy: 'workspace' });

// Traverse project + workspace + global config directory
const client = createConfiger({ moduleName: 'app', searchStrategy: 'global' });

Config Inheritance

Create a base config (base.config.json):

{ "logLevel": "info", "retries": 1 }

Extend it in your app config (.my-apprc.json):

{
  "extends": "./base.config.json",
  "retries": 3
}

Result: { logLevel: "info", retries: 3 } with sources tracking the full chain.

Environment Overrides

{
  "apiUrl": "https://api.default.com",
  "$development": { "apiUrl": "https://dev.api.com" },
  "$env": {
    "production": { "apiUrl": "https://prod.api.com" }
  }
}

const client = createConfiger({
  moduleName: 'app',
  envName: 'development', // or reads NODE_ENV automatically
});

Schema Validation

import type { ISchemaDescriptor } from '@elsikora/configer';

const schema: ISchemaDescriptor<{ serviceName: string; retryCount: number }> = {
  type: 'object',
  properties: {
    serviceName: { type: 'string', isRequired: true },
    retryCount: { type: 'number', defaultValue: 3 },
  },
  shouldAllowUnknownProperties: false,
};

const client = createConfiger({
  moduleName: 'app',
  schema,
});

Plugin Hooks

const client = createConfiger({
  moduleName: 'app',
  plugins: [
    {
      name: 'source-marker',
      afterRead: (result) => ({
        ...result,
        config: { ...result.config, _loadedFrom: result.filepath },
      }),
      onError: (error) => console.error('Config error:', error.message),
    },
  ],
});

Custom Loaders

const client = createConfiger({
  moduleName: 'app',
  searchPlaces: ['config.ini'],
  shouldMergeSearchPlaces: false,
  loaders: {
    '.ini': {
      asyncLoader: (_filepath, content) => parseIni(content),
      syncLoader: (_filepath, content) => parseIni(content),
    },
  },
});

Watch Mode

const handle = client.watchConfig((error, result) => {
  if (error) return console.error(error);
  console.log('Config changed:', result?.config);
});

// Cleanup on shutdown
process.on('SIGTERM', () => handle.close());

Reading from package.json

const client = createConfiger({
  moduleName: 'my-tool',
  packageProperty: 'config.myTool', // or ['config', 'myTool']
  searchPlaces: ['package.json'],
  shouldMergeSearchPlaces: false,
});

🛣 Roadmap

❓ FAQ

🔒 License

This project is licensed under MIT.

🙏 Acknowledgments

• Inspired by cosmiconfig — the gold standard for config file discovery in the Node.js ecosystem
• Built with @elsikora/cladi — a lightweight dependency injection container
• Parsing powered by yaml, smol-toml, json5, jsonc-parser, and dotenv
• Testing with Vitest and @elsikora/cladi-testing
• Thanks to the open-source community for feedback and inspiration

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