@fluojs/config

@fluojs/config

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Configuration loading, merging, validation, and typed runtime access for fluo applications.

Table of Contents

• Installation
• When to Use
• Quick Start
• Key Capabilities
• Public API
• Related Packages
• Example Sources

Installation

npm install @fluojs/config

When to Use

Use this package when you need to:

• Load configuration from .env files and environment variables.
• Merge multiple configuration sources with strict precedence rules.
• Validate your application configuration at startup.
• Access configuration values through a typed ConfigService.

Quick Start

The ConfigModule handles loading and validating your configuration during bootstrap.

import { Module } from '@fluojs/core';
import { ConfigModule } from '@fluojs/config';

@Module({
  imports: [
    ConfigModule.forRoot({
      envFile: '.env',
      processEnv: {
        DATABASE_URL: process.env.DATABASE_URL,
      },
      defaults: { PORT: '3000' },
      validate: (config) => {
        if (!config.DATABASE_URL) throw new Error('DATABASE_URL is required');
        return config;
      },
    }),
  ],
})
class AppModule {}

Once registered, you can inject ConfigService to access your values:

import { Inject } from '@fluojs/core';
import { ConfigService } from '@fluojs/config';

class MyService {
  constructor(@Inject(ConfigService) private config: ConfigService) {
    const port = this.config.get('PORT');
    const dbUrl = this.config.getOrThrow('DATABASE_URL');
  }
}

Key Capabilities

Source Precedence

Configuration is merged in the following order (highest precedence wins):

• Runtime Overrides: Values passed explicitly via runtimeOverrides.
• Process Environment Snapshot: Values passed via the processEnv option.
• Environment File: Values from the .env file (or custom path).
• Defaults: Values provided in the defaults option.

@fluojs/config does not scan ambient environment variables automatically. Pass an explicit processEnv snapshot at the bootstrap boundary when process-backed values should participate in precedence.

Deep Merging

Plain objects are deep-merged by key. Arrays and primitive values from higher-precedence sources completely replace lower-precedence ones.

Validation

The validate function runs after all sources are merged but before the application starts. If it throws, the application bootstrap fails immediately.

Runtime Access and Reload Cost Model

ConfigService.get('a.b.c') resolves dot-path keys by walking each path segment, so lookup cost is proportional to path depth. When get(), getOrThrow(), or snapshot() returns an object-like value, the returned value is a detached clone; clone cost is proportional to the returned subtree size so caller mutations cannot affect the active config snapshot.

ConfigReloadManager.reload() serializes reload work. If another reload is requested while the current reload is notifying listeners, the follow-up reload is queued and applied after the active notification finishes; if the active notification fails, the previous snapshot is restored and the queued reload is discarded. The same serialization and rollback contract applies to createConfigReloader(...).reload(), including manual reloads queued during watch-triggered notifications.

Public API

Class/Helper	Description
ConfigModule	Module for registering configuration globally or locally.
ConfigReloadModule	Registers the reload manager and exports the shared CONFIG_RELOADER token for dependency injection.
ConfigReloadManager	Coordinates reloads for the injected ConfigService, preserving service identity while replacing snapshots through the reload path.
CONFIG_RELOADER	Injection token for the shared config reloader contract.
ConfigService	Read-only service for typed access to configuration values. Snapshot replacement stays inside the config reload path.
loadConfig(options)	Functional entry point for loading configuration manually.
createConfigReloader(options)	Creates a reloader for dynamic configuration updates.

ConfigReloadManager.reload() updates the existing ConfigService instance so consumers keep their injected service identity while observing the new snapshot. If a reload listener throws, the manager restores the previous snapshot and rethrows the listener error. createConfigReloader(...).reload() follows the same listener serialization and rollback behavior for its standalone reloader snapshot.

Related Packages

• @fluojs/runtime: Calls loadConfig internally during application bootstrap.
• @fluojs/validation: Can be used within the validate function for schema-based validation.

Example Sources

• packages/config/src/load.ts
• packages/config/src/service.ts
• packages/config/src/load.test.ts