tapable

What is tapable?

The tapable package provides a collection of classes that can be used to add hooks into a plugin system. These hooks can be used to intercept and modify the behavior of certain functions or events, allowing for a highly customizable and extensible architecture. It is commonly used in webpack's plugin system but can be used in any JavaScript project to add similar plugin capabilities.

What are tapable's main functionalities?

SyncHook

SyncHook allows for synchronous execution of multiple functions. It is useful when you need to ensure that hooks are executed in the order they were added.

const { SyncHook } = require('tapable');

const hook = new SyncHook(['arg1', 'arg2']);

hook.tap('MyPlugin', (arg1, arg2) => {
  console.log(`Values received: ${arg1}, ${arg2}`);
});

hook.call('Hello', 'World');

AsyncParallelHook

AsyncParallelHook allows for asynchronous execution of hooks in parallel. It is useful when you have multiple asynchronous tasks that can run at the same time without waiting for each other.

const { AsyncParallelHook } = require('tapable');

const asyncHook = new AsyncParallelHook(['arg1']);

asyncHook.tapPromise('AsyncPlugin', (arg1) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log(`Async value: ${arg1}`);
      resolve();
    }, 1000);
  });
});

asyncHook.promise('Hello').then(() => {
  console.log('All async plugins have finished.');
});

AsyncSeriesHook

AsyncSeriesHook allows for asynchronous execution of hooks one after another. It is useful when tasks need to be done in a specific sequence, with each task starting only after the previous one has completed.

const { AsyncSeriesHook } = require('tapable');

const asyncSeriesHook = new AsyncSeriesHook(['arg1']);

asyncSeriesHook.tapPromise('AsyncSeriesPlugin', (arg1) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log(`Async series value: ${arg1}`);
      resolve();
    }, 1000);
  });
});

asyncSeriesHook.promise('World').then(() => {
  console.log('All async series plugins have finished.');
});

Other packages similar to tapable

eventemitter3

EventEmitter3 is a high-performance event emitter. It provides similar functionality to Tapable in that it allows you to emit and listen for events, but it does not offer the same plugin/hook system that Tapable does.

mitt

Mitt is a tiny functional event emitter / pubsub. It provides similar event handling capabilities but lacks the hook system that allows for interception and modification of behavior, which is a key feature of Tapable.

rxjs

RxJS is a library for reactive programming using Observables. It can be used to handle asynchronous data streams and events similar to Tapable's hooks, but it is more focused on functional reactive programming patterns and is more complex.

README

Tapable

The tapable packages exposes many Hook classes, which can be used to create hooks for plugins.

const {
	SyncHook,
	SyncBailHook,
	SyncWaterfallHook,
	SyncLoopHook,
	AsyncParallelHook,
	AsyncParallelBailHook,
	AsyncSequencialHook,
	AsyncSequencialBailHook,
	AsyncWaterfallHook
 } = require("tapable");

Usage

All Hook constructors take one optional argument, which is a list of argument names as strings.

const hook = new SyncHook(["arg1", "arg2", "arg3"]);

The best practice is to expose all hooks of a class in a hooks property:

class Car {
	constructor() {
		this.hooks = {
			accelerate: new SyncHook(["newSpeed"]),
			break: new SyncHook(),
			calculateRoutes: new AsyncParallelHook(["source", "target", "routesList"])
		};
	}

	/* ... */
}

Other people can now use these hooks:

const myCar = new Car();

// Use the tap method to add a consument
myCar.hooks.break.tap("WarningLampPlugin", () => warningLamp.on());

It's required to pass a name to identify the plugin/reason.

You may receive arguments:

myCar.hooks.accelerate.tap("LoggerPlugin", newSpeed => console.log(`Accelerating to ${newSpeed}`));

For sync hooks tap is the only valid method to add a plugin. Async hooks also support async plugins:

myCar.hooks.calculateRoutes.tapPromise("GoogleMapsPlugin", (source, target, routesList) => {
	// return a promise
	return google.maps.findRoute(source, target).then(route => {
		routesList.add(route);
	});
});
myCar.hooks.calculateRoutes.tapAsync("BingMapsPlugin", (source, target, routesList, callback) => {
	bing.findRoute(source, target, (err, route) => {
		if(err) return callback(err);
		routesList.add(route);
		// call the callback
		callback();
	});
});

// You can still use sync plugins
myCar.hooks.calculateRoutes.tap("CachedRoutesPlugin", (source, target, routesList) => {
	const cachedRoute = cache.get(source, target);
	if(cachedRoute)
		routesList.add(cachedRoute);
})

The class declaring these hooks need to call them:

class Car {
	/* ... */

	setSpeed(newSpeed) {
		this.hooks.accelerate.call(newSpeed);
	}

	useNavigationSystemPromise(source, target) {
		const routesList = new List();
		return this.hooks.calculateRoutes.promise(source, target, routesList).then(() => {
			return routesList.getRoutes();
		});
	}

	useNavigationSystemAsync(source, target, callback) {
		const routesList = new List();
		this.hooks.calculateRoutes.callAsync(source, target, routesList, err => {
			if(err) return callback(err);
			callback(null, routesList.getRoutes());
		});
	}
}

The Hook will compile a method with the most efficient way of running your plugins. It generates code depending on:

• The number of registered plugins (none, one, many)
• The kind of registered plugins (sync, async, promise)
• The used call method (sync, async, promise)
• The number of arguments
• Whether interception is used

This ensures fastest possible execution.

Interception

All Hooks offer an additional interception API:

myCar.hooks.calculateRoutes.intercept({
	call: (source, target, routesList) => {
		console.log("Starting to calculate routes");
	},
	tap: (tapInfo) => {
		// tapInfo = { type: "promise", name: "GoogleMapsPlugin", fn: ... }
		console.log(`${tapInfo.name} is doing it's job`);
		return tapInfo; // may return a new tapInfo object
	}
})