@moduul/core

Core plugin host system for dynamically loading and managing plugins at runtime.

Features

• 🔌 Dynamic Plugin Loading - Load plugins from directories or ZIP archives at runtime
• � Single-Plugin Mode - Point directly at one plugin directory instead of scanning a folder
• �🔥 Hot Reload - Cache-busting support for plugin reloading during development
• 📦 Multiple Formats - Support for both ESM and CommonJS plugins
• ✅ Validation - Built-in manifest validation with optional custom validators
• 🎯 Type-Safe - Full TypeScript support with comprehensive type definitions
• 🚀 Zero Config - Works out of the box with sensible defaults

Installation

npm install @moduul/core

Quick Start

Folder mode (scan a directory of plugins)

import { PluginHost } from '@moduul/core';

// Define your plugin interface for type safety
interface MyPlugin {
  execute(): Promise<string>;
}

// Create a typed plugin host pointing at a folder of plugin subdirectories
const host = new PluginHost<MyPlugin>({
  folder: './plugins'
});

// Load all plugins found in the folder
await host.reload();

// Get all loaded plugins (typed!)
const plugins = host.getAll();
console.log(`Loaded ${plugins.length} plugins`);

// Find a specific plugin
const plugin = host.find('my-plugin');
if (plugin) {
  // Full type safety and autocomplete
  const result = await plugin.plugin.execute();
  console.log(result);
}

Single-plugin mode (load one plugin directly)

import { PluginHost } from '@moduul/core';

interface MyPlugin {
  execute(): Promise<string>;
}

// Point directly at a single plugin directory
const host = new PluginHost<MyPlugin>({
  pluginPath: '/absolute/path/to/my-plugin'
});

await host.reload();

const plugin = host.find('my-plugin');
if (plugin) {
  const result = await plugin.plugin.execute();
  console.log(result);
}

API Reference

PluginHost<T>

The main class for managing plugins. Supports a generic type parameter T to define the expected plugin interface, enabling full type safety and IDE autocomplete.

Generic Type Parameter

The PluginHost class accepts a generic type parameter that defines the shape of your plugins:

// Define your plugin interface
interface MyPlugin {
  name: string;
  version: string;
  execute(input: string): Promise<string>;
}

// Create a typed host
const host = new PluginHost<MyPlugin>({
  folder: './plugins'
});

// Type-safe access to plugins
await host.reload();
const plugin = host.find('my-plugin');
if (plugin) {
  // TypeScript knows plugin.plugin is MyPlugin
  const result = await plugin.plugin.execute('hello'); // ✓ Type-checked
  console.log(plugin.plugin.name); // ✓ Autocomplete works
}

Benefits of using the generic type:

• Type Safety: Catch errors at compile time instead of runtime
• IDE Support: Full autocomplete and IntelliSense for plugin methods
• Documentation: Self-documenting code with clear contracts
• Refactoring: Safe refactoring with TypeScript's rename/find references

Without generic type (untyped):

const host = new PluginHost({ folder: './plugins' });
const plugin = host.find('my-plugin');
if (plugin) {
  // plugin.plugin is `unknown` - no type safety
  const result = await (plugin.plugin as any).execute('hello'); // No autocomplete
}

Constructor

new PluginHost<T>(options: PluginHostOptions<T>)

PluginHostOptions<T> is a union type with two mutually exclusive modes:

Folder mode — scan a directory for plugin subdirectories (or .zip archives):

| Option | Type | Required | Description | |---|---|---|---| | folder | string | ✓ | Path to the directory that contains plugin subdirectories or .zip archives | | validator | (plugin: unknown) => plugin is T | | Type guard to validate each loaded plugin |

Single-plugin mode — load exactly one plugin from a specific directory:

| Option | Type | Required | Description | |---|---|---|---| | pluginPath | string | ✓ | Path to a single plugin directory (must contain plugin.manifest.json) | | validator | (plugin: unknown) => plugin is T | | Type guard to validate the loaded plugin |

The two modes are mutually exclusive: use either folder or pluginPath, never both.

Example — folder mode with validator:

interface MyPlugin {
  execute(): string;
  version: string;
}

const host = new PluginHost<MyPlugin>({
  folder: './plugins',
  // Type guard that validates plugin structure
  validator: (plugin): plugin is MyPlugin => {
    return (
      typeof plugin === 'object' &&
      plugin !== null &&
      typeof (plugin as any).execute === 'function' &&
      typeof (plugin as any).version === 'string'
    );
  }
});

Example — single-plugin mode with validator:

const host = new PluginHost<MyPlugin>({
  pluginPath: '/opt/plugins/my-plugin',
  validator: (plugin): plugin is MyPlugin => {
    return (
      typeof plugin === 'object' &&
      plugin !== null &&
      typeof (plugin as any).execute === 'function' &&
      typeof (plugin as any).version === 'string'
    );
  }
});

The validator acts as a TypeScript type guard, narrowing unknown to T.

Methods

reload(): Promise<void>

Scans the plugin folder and loads all valid plugins. Clears previously loaded plugins.

await host.reload();

getAll(): LoadedPlugin<T>[]

Returns an array of all loaded plugins with full type information.

interface MyPlugin {
  execute(): string;
}

const host = new PluginHost<MyPlugin>({ folder: './plugins' });
await host.reload();

const plugins = host.getAll();
plugins.forEach(({ manifest, plugin }) => {
  console.log(`${manifest.name} v${manifest.version}`);
  // plugin is typed as MyPlugin
  const result = plugin.execute(); // ✓ Type-safe
});

find(name: string): LoadedPlugin<T> | undefined

Finds a plugin by name with full type information.

const plugin = host.find('my-plugin');
if (plugin) {
  // plugin is typed as LoadedPlugin<MyPlugin>
  console.log('Found:', plugin.manifest.name);
  const result = await plugin.plugin.execute(); // ✓ Autocomplete works
}

Types

PluginManifest

The required structure for plugin.manifest.json:

interface PluginManifest {
  name: string;           // Unique plugin identifier
  version: string;        // Semantic version
  entryPoint: string;     // Relative path to main file (e.g., "./dist/index.js")
  meta?: {                // Optional metadata
    description?: string;
    author?: string;
    [key: string]: unknown;
  };
}

LoadedPlugin<T>

The structure returned by getAll() and find():

interface LoadedPlugin<T> {
  manifest: PluginManifest;  // Parsed manifest
  plugin: T;                 // The loaded module (typed)
}

Example usage:

interface MyPlugin {
  execute(): string;
}

const host = new PluginHost<MyPlugin>({ folder: './plugins' });
const plugin: LoadedPlugin<MyPlugin> | undefined = host.find('test');

PluginHostOptions<T>

Union of PluginHostFolderOptions<T> and PluginHostSingleOptions<T>.

// Folder scan mode
interface PluginHostFolderOptions<T> {
  folder: string;                                // Directory containing plugin subdirectories / ZIPs
  validator?: (plugin: unknown) => plugin is T;  // Optional type guard
}

// Single-plugin mode
interface PluginHostSingleOptions<T> {
  pluginPath: string;                            // Path to one plugin directory
  validator?: (plugin: unknown) => plugin is T;  // Optional type guard
}

type PluginHostOptions<T> = PluginHostFolderOptions<T> | PluginHostSingleOptions<T>;

Both constituent types are exported and can be used for narrowing or explicit annotation.

Plugin Structure

A valid plugin must have:

1. plugin.manifest.json - Manifest file at the root
2. Entry point - The JavaScript file specified in entryPoint

Directory Plugin Example

my-plugin/
├── plugin.manifest.json
└── dist/
    └── index.js

plugin.manifest.json:

{
  "name": "my-plugin",
  "version": "1.0.0",
  "entryPoint": "./dist/index.js",
  "meta": {
    "description": "My awesome plugin",
    "author": "Your Name"
  }
}

dist/index.js:

export default {
  name: 'my-plugin',
  execute() {
    console.log('Hello from plugin!');
  }
};

ZIP Archive Support

Plugins can be distributed as .zip files. The host automatically extracts them to a temporary directory before loading.

plugins/
├── my-plugin/           # Directory plugin
└── another-plugin.zip   # ZIP archive plugin

Module Formats

ESM Plugins (Recommended)

package.json:

{
  "type": "module"
}

index.js:

export default {
  execute() {
    return 'result';
  }
};

CommonJS Plugins

index.js:

module.exports = {
  execute() {
    return 'result';
  }
};

Custom Validation

Add a validator to enforce plugin structure at runtime and enable type narrowing:

interface MyPlugin {
  name: string;
  execute(): Promise<string>;
  version: string;
}

const host = new PluginHost<MyPlugin>({
  folder: './plugins',
  // Type guard validates and narrows type from unknown to MyPlugin
  validator: (plugin): plugin is MyPlugin => {
    return (
      typeof plugin === 'object' &&
      plugin !== null &&
      typeof (plugin as any).name === 'string' &&
      typeof (plugin as any).execute === 'function' &&
      typeof (plugin as any).version === 'string'
    );
  }
});

await host.reload();

// All plugins are guaranteed to match MyPlugin interface
const plugins = host.getAll();
plugins.forEach(({ plugin }) => {
  // TypeScript knows these properties exist
  console.log(`${plugin.name} v${plugin.version}`);
});

Pro Tip: Use a validation library like zod for more robust validation:

import { z } from 'zod';

const PluginSchema = z.object({
  name: z.string(),
  version: z.string(),
  execute: z.function().returns(z.promise(z.string())),
});

type MyPlugin = z.infer<typeof PluginSchema>;

const host = new PluginHost<MyPlugin>({
  folder: './plugins',
  validator: (plugin): plugin is MyPlugin => {
    return PluginSchema.safeParse(plugin).success;
  }
});

Error Handling

The plugin host gracefully handles errors:

• Invalid manifests - Logged and skipped
• Missing entry points - Logged and skipped
• Import errors - Logged and skipped
• Validation failures - Logged and skipped

Errors are logged to console.warn and don't crash the host.

Hot Reload

Cache busting is automatic. Each reload() call uses a new timestamp:

// Development workflow
while (developing) {
  // Make changes to plugin...
  
  await host.reload(); // Loads fresh version
  
  const plugin = host.find('my-plugin');
  await plugin.plugin.execute();
}

Dual-Format Package

@moduul/core is published in both ESM and CommonJS formats:

// ESM
import { PluginHost } from '@moduul/core';

// CommonJS
const { PluginHost } = require('@moduul/core');

TypeScript Support

Full type definitions included with generic type support. All option types are exported:

import { PluginHost, PluginManifest, LoadedPlugin, PluginHostFolderOptions, PluginHostSingleOptions } from '@moduul/core';

// Define your plugin interface
interface MyPlugin {
  execute(input: string): Promise<string>;
  cleanup?(): Promise<void>;
}

// Create typed host
const host: PluginHost<MyPlugin> = new PluginHost<MyPlugin>({ 
  folder: './plugins' 
});

// Type-safe plugin access
const plugins: LoadedPlugin<MyPlugin>[] = host.getAll();

// Type guard validator
const validator = (plugin: unknown): plugin is MyPlugin => {
  return (
    typeof plugin === 'object' &&
    plugin !== null &&
    typeof (plugin as any).execute === 'function'
  );
};

// Manifest typing
const manifest: PluginManifest = {
  name: 'my-plugin',
  version: '1.0.0',
  entryPoint: './dist/index.js'
};

Advanced: Multiple Plugin Types

// Define base interface
interface BasePlugin {
  name: string;
  version: string;
}

// Define specific plugin types
interface DataPlugin extends BasePlugin {
  processData(data: unknown): Promise<unknown>;
}

interface UIPlugin extends BasePlugin {
  render(): HTMLElement;
}

// Create separate hosts for different plugin types
const dataHost = new PluginHost<DataPlugin>({
  folder: './plugins/data',
  validator: (p): p is DataPlugin => 
    typeof (p as any)?.processData === 'function'
});

const uiHost = new PluginHost<UIPlugin>({
  folder: './plugins/ui',
  validator: (p): p is UIPlugin => 
    typeof (p as any)?.render === 'function'
});

Requirements

• Node.js 20 or higher
• ESM support (built-in)

Related Packages

• @moduul/builder - CLI tool for building plugins
• @moduul/boilerplate - Official plugin template

License

MIT