Event Emitting and Middleware Hooks

Features

• Simple replacement for EventEmitter
• Async / Sync Middleware Hooks for Your Methods
• ESM / CJS with Types and Nodejs 20+
• Browser Support and Delivered via CDN
• Ability to throw errors in hooks
• Ability to pass in a logger (such as Pino) for errors
• Enforce consistent hook naming conventions with enforceBeforeAfter
• Deprecation warnings for hooks with deprecatedHooks
• Control deprecated hook execution with allowDeprecated
• No package dependencies and only 100KB in size
• Fast and Efficient with Benchmarks
• Maintained on a regular basis!

Table of Contents

• Installation
• Usage
• Using it in the Browser
• API - Hooks
  • .throwHookErrors
  • .logger
  • .enforceBeforeAfter
  • .deprecatedHooks
  • .allowDeprecated
  • .onHook(eventName, handler)
  • .onHookEntry(hookEntry)
  • .addHook(eventName, handler)
  • .onHooks(Array)
  • .onceHook(eventName, handler)
  • .prependHook(eventName, handler)
  • .prependOnceHook(eventName, handler)
  • .removeHook(eventName)
  • .removeHooks(Array)
  • .hook(eventName, ...args)
  • .callHook(eventName, ...args)
  • .beforeHook(eventName, ...args)
  • .afterHook(eventName, ...args)
  • .hooks
  • .getHooks(eventName)
  • .clearHooks(eventName)
• API - Events
  • .throwOnEmitError
  • .on(eventName, handler)
  • .off(eventName, handler)
  • .emit(eventName, ...args)
  • .listeners(eventName)
  • .removeAllListeners(eventName)
  • .setMaxListeners(maxListeners: number)
  • .once(eventName, handler)
  • .prependListener(eventName, handler)
  • .prependOnceListener(eventName, handler)
  • .eventNames()
  • .listenerCount(eventName?)
  • .rawListeners(eventName?)
• Benchmarks
• How to Contribute
• License and Copyright

Installation

npm install hookified --save

Usage

This was built because we constantly wanted hooks and events extended on libraires we are building such as Keyv and Cacheable. This is a simple way to add hooks and events to your classes.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World'); //using Emittery
  }

  //with hooks you can pass data in and if they are subscribed via onHook they can modify the data
  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

You can even pass in multiple arguments to the hooks:

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    let data2 = { some: 'data2' };
    // do something
    await this.hook('before:myMethod2', data, data2);

    return data;
  }
}

Using it in the Browser

<script type="module">
  import { Hookified } from 'https://cdn.jsdelivr.net/npm/hookified/dist/browser/index.js';

  class MyClass extends Hookified {
    constructor() {
      super();
    }

    async myMethodEmittingEvent() {
      this.emit('message', 'Hello World'); //using Emittery
    }

    //with hooks you can pass data in and if they are subscribed via onHook they can modify the data
    async myMethodWithHooks() Promise<any> {
      let data = { some: 'data' };
      // do something
      await this.hook('before:myMethod2', data);

      return data;
    }
  }
</script>

if you are not using ESM modules, you can use the following:

<script src="https://cdn.jsdelivr.net/npm/hookified/dist/browser/index.global.js"></script>
<script>
  class MyClass extends Hookified {
    constructor() {
      super();
    }

    async myMethodEmittingEvent() {
      this.emit('message', 'Hello World'); //using Emittery
    }

    //with hooks you can pass data in and if they are subscribed via onHook they can modify the data
    async myMethodWithHooks() Promise<any> {
      let data = { some: 'data' };
      // do something
      await this.hook('before:myMethod2', data);

      return data;
    }
  }
</script>

API - Hooks

.throwHookErrors

If set to true, errors thrown in hooks will be thrown. If set to false, errors will be only emitted.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super({ throwHookErrors: true });
  }
}

const myClass = new MyClass();

console.log(myClass.throwHookErrors); // true. because it is set in super

try {
  myClass.onHook('error-event', async () => {
    throw new Error('error');
  });

  await myClass.hook('error-event');
} catch (error) {
  console.log(error.message); // error
}

myClass.throwHookErrors = false;
console.log(myClass.throwHookErrors); // false

.logger

If set, errors thrown in hooks will be logged to the logger. If not set, errors will be only emitted.

import { Hookified } from 'hookified';
import pino from 'pino';

const logger = pino(); // create a logger instance that is compatible with Logger type

class MyClass extends Hookified {
  constructor() {
    super({ logger });
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async () => {
  throw new Error('error');
});

// when you call before:myMethod2 it will log the error to the logger
await myClass.hook('before:myMethod2');

.enforceBeforeAfter

If set to true, enforces that all hook names must start with ‘before’ or ‘after’. This is useful for maintaining consistent hook naming conventions in your application. Default is false.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super({ enforceBeforeAfter: true });
  }
}

const myClass = new MyClass();

console.log(myClass.enforceBeforeAfter); // true

// These will work fine
myClass.onHook('beforeSave', async () => {
  console.log('Before save hook');
});

myClass.onHook('afterSave', async () => {
  console.log('After save hook');
});

myClass.onHook('before:validation', async () => {
  console.log('Before validation hook');
});

// This will throw an error
try {
  myClass.onHook('customEvent', async () => {
    console.log('This will not work');
  });
} catch (error) {
  console.log(error.message); // Hook event "customEvent" must start with "before" or "after" when enforceBeforeAfter is enabled
}

// You can also change it dynamically
myClass.enforceBeforeAfter = false;
myClass.onHook('customEvent', async () => {
  console.log('This will work now');
});

The validation applies to all hook-related methods:

• onHook(), addHook(), onHookEntry(), onHooks()
• prependHook(), onceHook(), prependOnceHook()
• hook(), callHook()
• getHooks(), removeHook(), removeHooks()

Note: The beforeHook() and afterHook() helper methods automatically generate proper hook names and work regardless of the enforceBeforeAfter setting.

.deprecatedHooks

A Map of deprecated hook names to deprecation messages. When a deprecated hook is used, a warning will be emitted via the ‘warn’ event and logged to the logger (if available). Default is an empty Map.

import { Hookified } from 'hookified';

// Define deprecated hooks with custom messages
const deprecatedHooks = new Map([
  ['oldHook', 'Use newHook instead'],
  ['legacyMethod', 'This hook will be removed in v2.0'],
  ['deprecatedFeature', ''] // Empty message - will just say "deprecated"
]);

class MyClass extends Hookified {
  constructor() {
    super({ deprecatedHooks });
  }
}

const myClass = new MyClass();

console.log(myClass.deprecatedHooks); // Map with deprecated hooks

// Listen for deprecation warnings
myClass.on('warn', (event) => {
  console.log(`Deprecation warning: ${event.message}`);
  // event.hook contains the hook name
  // event.message contains the full warning message
});

// Using a deprecated hook will emit warnings
myClass.onHook('oldHook', () => {
  console.log('This hook is deprecated');
});
// Output: Hook "oldHook" is deprecated: Use newHook instead

// Using a deprecated hook with empty message
myClass.onHook('deprecatedFeature', () => {
  console.log('This hook is deprecated');
});
// Output: Hook "deprecatedFeature" is deprecated

// You can also set deprecated hooks dynamically
myClass.deprecatedHooks.set('anotherOldHook', 'Please migrate to the new API');

// Works with logger if provided
import pino from 'pino';
const logger = pino();

const myClassWithLogger = new Hookified({ 
  deprecatedHooks,
  logger 
});

// Deprecation warnings will be logged to logger.warn

The deprecation warning system applies to all hook-related methods:

• Registration: onHook(), addHook(), onHookEntry(), onHooks(), prependHook(), onceHook(), prependOnceHook()
• Execution: hook(), callHook()
• Management: getHooks(), removeHook(), removeHooks()

Deprecation warnings are emitted in two ways:

1. Event: A ‘warn’ event is emitted with { hook: string, message: string }
2. Logger: Logged to logger.warn() if a logger is configured and has a warn method

.allowDeprecated

Controls whether deprecated hooks are allowed to be registered and executed. Default is true. When set to false, deprecated hooks will still emit warnings but will be prevented from registration and execution.

import { Hookified } from 'hookified';

const deprecatedHooks = new Map([
  ['oldHook', 'Use newHook instead']
]);

class MyClass extends Hookified {
  constructor() {
    super({ deprecatedHooks, allowDeprecated: false });
  }
}

const myClass = new MyClass();

console.log(myClass.allowDeprecated); // false

// Listen for deprecation warnings (still emitted even when blocked)
myClass.on('warn', (event) => {
  console.log(`Warning: ${event.message}`);
});

// Try to register a deprecated hook - will emit warning but not register
myClass.onHook('oldHook', () => {
  console.log('This will never execute');
});
// Output: Warning: Hook "oldHook" is deprecated: Use newHook instead

// Verify hook was not registered
console.log(myClass.getHooks('oldHook')); // undefined

// Try to execute a deprecated hook - will emit warning but not execute
await myClass.hook('oldHook');
// Output: Warning: Hook "oldHook" is deprecated: Use newHook instead
// (but no handlers execute)

// Non-deprecated hooks work normally
myClass.onHook('validHook', () => {
  console.log('This works fine');
});

console.log(myClass.getHooks('validHook')); // [handler function]

// You can dynamically change the setting
myClass.allowDeprecated = true;

// Now deprecated hooks can be registered and executed
myClass.onHook('oldHook', () => {
  console.log('Now this works');
});

console.log(myClass.getHooks('oldHook')); // [handler function]

Behavior when allowDeprecated is false:

• Registration: All hook registration methods (onHook, addHook, prependHook, etc.) will emit warnings but skip registration
• Execution: Hook execution methods (hook, callHook) will emit warnings but skip execution
• Management: Hook management methods (getHooks, removeHook) will emit warnings and return undefined/skip operations
• Warnings: Deprecation warnings are always emitted regardless of allowDeprecated setting

Use cases:

• Development: Keep allowDeprecated: true to maintain functionality while seeing warnings
• Testing: Set allowDeprecated: false to ensure no deprecated hooks are accidentally used
• Migration: Gradually disable deprecated hooks during API transitions
• Production: Disable deprecated hooks to prevent legacy code execution

.onHook(eventName, handler)

Subscribe to a hook event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});

.onHookEntry(hookEntry)

This allows you to create a hook with the HookEntry type which includes the event and handler. This is useful for creating hooks with a single object.

import { Hookified, HookEntry } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHookEntry({
  event: 'before:myMethod2',
  handler: async (data) => {
    data.some = 'new data';
  },
});

.addHook(eventName, handler)

This is an alias for .onHook(eventName, handler) for backwards compatibility.

.onHooks(Array)

Subscribe to multiple hook events at once

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    await this.hook('before:myMethodWithHooks', data);
    
    // do something here with the data
    data.some = 'new data';

    await this.hook('after:myMethodWithHooks', data);

    return data;
  }
}

const myClass = new MyClass();
const hooks = [
  {
    event: 'before:myMethodWithHooks',
    handler: async (data) => {
      data.some = 'new data1';
    },
  },
  {
    event: 'after:myMethodWithHooks',
    handler: async (data) => {
      data.some = 'new data2';
    },
  },
];

.onceHook(eventName, handler)

Subscribe to a hook event once.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();

myClass.onHookOnce('before:myMethod2', async (data) => {
  data.some = 'new data';
});

myClass.myMethodWithHooks();

console.log(myClass.hooks.length); // 0

.prependHook(eventName, handler)

Subscribe to a hook event before all other hooks.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});
myClass.preHook('before:myMethod2', async (data) => {
  data.some = 'will run before new data';
});

.prependOnceHook(eventName, handler)

Subscribe to a hook event before all other hooks. After it is used once it will be removed.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});
myClass.preHook('before:myMethod2', async (data) => {
  data.some = 'will run before new data';
});

.removeHook(eventName)

Unsubscribe from a hook event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
const handler = async (data) => {
  data.some = 'new data';
};

myClass.onHook('before:myMethod2', handler);

myClass.removeHook('before:myMethod2', handler);

.removeHooks(Array)

Unsubscribe from multiple hooks.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    await this.hook('before:myMethodWithHooks', data);
    
    // do something
    data.some = 'new data';
    await this.hook('after:myMethodWithHooks', data);

    return data;
  }
}

const myClass = new MyClass();

const hooks = [
  {
    event: 'before:myMethodWithHooks',
    handler: async (data) => {
      data.some = 'new data1';
    },
  },
  {
    event: 'after:myMethodWithHooks',
    handler: async (data) => {
      data.some = 'new data2';
    },
  },
];
myClass.onHooks(hooks);

// remove all hooks
myClass.removeHook(hooks);

.hook(eventName, ...args)

Run a hook event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

in this example we are passing multiple arguments to the hook:

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    let data2 = { some: 'data2' };
    // do something
    await this.hook('before:myMethod2', data, data2);

    return data;
  }
}

const myClass = new MyClass();

myClass.onHook('before:myMethod2', async (data, data2) => {
  data.some = 'new data';
  data2.some = 'new data2';
});

await myClass.myMethodWithHooks();

.callHook(eventName, ...args)

This is an alias for .hook(eventName, ...args) for backwards compatibility.

.beforeHook(eventName, ...args)

This is a helper function that will prepend a hook name with before:.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // the event name will be `before:myMethod2`
    await this.beforeHook('myMethod2', data);

    return data;
  }
}

.afterHook(eventName, ...args)

This is a helper function that will prepend a hook name with after:.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // the event name will be `after:myMethod2`
    await this.afterHook('myMethod2', data);

    return data;
  }
}

.hooks

Get all hooks.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});

console.log(myClass.hooks);

.getHooks(eventName)

Get all hooks for an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();
myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});

console.log(myClass.getHooks('before:myMethod2'));

.clearHooks(eventName)

Clear all hooks for an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

const myClass = new MyClass();

myClass.onHook('before:myMethod2', async (data) => {
  data.some = 'new data';
});

myClass.clearHooks('before:myMethod2');

API - Events

.throwOnEmitError

If set to true, errors emitted as error will be thrown if there are no listeners. If set to false, errors will be only emitted.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodWithHooks() Promise<any> {
    let data = { some: 'data' };
    // do something
    await this.hook('before:myMethod2', data);

    return data;
  }
}

.on(eventName, handler)

Subscribe to an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

.off(eventName, handler)

Unsubscribe from an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

const myClass = new MyClass();
myClass.on('message', (message) => {
  console.log(message);
});

myClass.off('message', (message) => {
  console.log(message);
});

.emit(eventName, ...args)

Emit an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

.listeners(eventName)

Get all listeners for an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

console.log(myClass.listeners('message'));

.removeAllListeners(eventName)

Remove all listeners for an event.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

myClass.removeAllListeners('message');

.setMaxListeners(maxListeners: number)

Set the maximum number of listeners and will truncate if there are already too many.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }

  async myMethodEmittingEvent() {
    this.emit('message', 'Hello World');
  }
}

const myClass = new MyClass();

myClass.setMaxListeners(1);

myClass.on('message', (message) => {
  console.log(message);
});

myClass.on('message', (message) => {
  console.log(message);
}); // this will not be added and console warning

console.log(myClass.listenerCount('message')); // 1

.once(eventName, handler)

Subscribe to an event once.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.once('message', (message) => {
  console.log(message);
});

myClass.emit('message', 'Hello World');

myClass.emit('message', 'Hello World'); // this will not be called

.prependListener(eventName, handler)

Prepend a listener to an event. This will be called before any other listeners.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.prependListener('message', (message) => {
  console.log(message);
});

.prependOnceListener(eventName, handler)

Prepend a listener to an event once. This will be called before any other listeners.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.prependOnceListener('message', (message) => {
  console.log(message);
});

myClass.emit('message', 'Hello World');

.eventNames()

Get all event names.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

console.log(myClass.eventNames());

.listenerCount(eventName?)

Get the count of listeners for an event or all events if evenName not provided.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

console.log(myClass.listenerCount('message')); // 1

.rawListeners(eventName?)

Get all listeners for an event or all events if evenName not provided.

import { Hookified } from 'hookified';

class MyClass extends Hookified {
  constructor() {
    super();
  }
}

const myClass = new MyClass();

myClass.on('message', (message) => {
  console.log(message);
});

console.log(myClass.rawListeners('message'));

Benchmarks

We are doing very simple benchmarking to see how this compares to other libraries using tinybench. This is not a full benchmark but just a simple way to see how it performs. Our goal is to be as close or better than the other libraries including native (EventEmitter).

Hooks

Emits

This shows how on par hookified is to the native EventEmitter and popular eventemitter3. These are simple emitting benchmarks to see how it performs.

Note: the EventEmitter version is Nodejs versioning.

How to Contribute

Hookified is written in TypeScript and tests are written in vitest. To run the tests, use the following command:

To setup the environment and run the tests:

pnpm i && pnpm test

Note that we are using pnpm as our package manager. If you don't have it installed, you can install it globally with:

npm install -g pnpm

To contribute follow the Contributing Guidelines and Code of Conduct.

pnpm i && pnpm test

Note that we are using pnpm as our package manager. If you don't have it installed, you can install it globally with:

npm install -g pnpm

To contribute follow the Contributing Guidelines and Code of Conduct.

License and Copyright

MIT & © Jared Wray