Tapable

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

1const {
2	SyncHook,
3	SyncBailHook,
4	SyncWaterfallHook,
5	SyncLoopHook,
6	AsyncParallelHook,
7	AsyncParallelBailHook,
8	AsyncSeriesHook,
9	AsyncSeriesBailHook,
10	AsyncSeriesWaterfallHook
11 } = require("tapable");

Installation

1npm install --save tapable

Usage

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

1const hook = new SyncHook(["arg1", "arg2", "arg3"]);

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

1class Car {
2	constructor() {
3		this.hooks = {
4			accelerate: new SyncHook(["newSpeed"]),
5			brake: new SyncHook(),
6			calculateRoutes: new AsyncParallelHook(["source", "target", "routesList"])
7		};
8	}
9
10	/* ... */
11}

Other people can now use these hooks:

1const myCar = new Car();
2
3// Use the tap method to add a consument
4myCar.hooks.brake.tap("WarningLampPlugin", () => warningLamp.on());

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

You may receive arguments:

1myCar.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:

1myCar.hooks.calculateRoutes.tapPromise("GoogleMapsPlugin", (source, target, routesList) => {
2	// return a promise
3	return google.maps.findRoute(source, target).then(route => {
4		routesList.add(route);
5	});
6});
7myCar.hooks.calculateRoutes.tapAsync("BingMapsPlugin", (source, target, routesList, callback) => {
8	bing.findRoute(source, target, (err, route) => {
9		if(err) return callback(err);
10		routesList.add(route);
11		// call the callback
12		callback();
13	});
14});
15
16// You can still use sync plugins
17myCar.hooks.calculateRoutes.tap("CachedRoutesPlugin", (source, target, routesList) => {
18	const cachedRoute = cache.get(source, target);
19	if(cachedRoute)
20		routesList.add(cachedRoute);
21})

The class declaring these hooks need to call them:

1class Car {
2	/**
3	  * You won't get returned value from SyncHook or AsyncParallelHook,
4	  * to do that, use SyncWaterfallHook and AsyncSeriesWaterfallHook respectively
5	 **/
6
7	setSpeed(newSpeed) {
8		// following call returns undefined even when you returned values
9		this.hooks.accelerate.call(newSpeed);
10	}
11
12	useNavigationSystemPromise(source, target) {
13		const routesList = new List();
14		return this.hooks.calculateRoutes.promise(source, target, routesList).then((res) => {
15			// res is undefined for AsyncParallelHook
16			return routesList.getRoutes();
17		});
18	}
19
20	useNavigationSystemAsync(source, target, callback) {
21		const routesList = new List();
22		this.hooks.calculateRoutes.callAsync(source, target, routesList, err => {
23			if(err) return callback(err);
24			callback(null, routesList.getRoutes());
25		});
26	}
27}

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.

Hook types

Each hook can be tapped with one or several functions. How they are executed depends on the hook type:

• Basic hook (without “Waterfall”, “Bail” or “Loop” in its name). This hook simply calls every function it tapped in a row.

• Waterfall. A waterfall hook also calls each tapped function in a row. Unlike the basic hook, it passes a return value from each function to the next function.

• Bail. A bail hook allows exiting early. When any of the tapped function returns anything, the bail hook will stop executing the remaining ones.

• Loop. When a plugin in a loop hook returns a non-undefined value the hook will restart from the first plugin. It will loop until all plugins return undefined.

Additionally, hooks can be synchronous or asynchronous. To reflect this, there’re “Sync”, “AsyncSeries”, and “AsyncParallel” hook classes:

• Sync. A sync hook can only be tapped with synchronous functions (using myHook.tap()).

• AsyncSeries. An async-series hook can be tapped with synchronous, callback-based and promise-based functions (using myHook.tap(), myHook.tapAsync() and myHook.tapPromise()). They call each async method in a row.

• AsyncParallel. An async-parallel hook can also be tapped with synchronous, callback-based and promise-based functions (using myHook.tap(), myHook.tapAsync() and myHook.tapPromise()). However, they run each async method in parallel.

The hook type is reflected in its class name. E.g., AsyncSeriesWaterfallHook allows asynchronous functions and runs them in series, passing each function’s return value into the next function.

Interception

All Hooks offer an additional interception API:

1myCar.hooks.calculateRoutes.intercept({
2	call: (source, target, routesList) => {
3		console.log("Starting to calculate routes");
4	},
5	register: (tapInfo) => {
6		// tapInfo = { type: "promise", name: "GoogleMapsPlugin", fn: ... }
7		console.log(`${tapInfo.name} is doing its job`);
8		return tapInfo; // may return a new tapInfo object
9	}
10})

call: (...args) => void Adding call to your interceptor will trigger when hooks are triggered. You have access to the hooks arguments.

tap: (tap: Tap) => void Adding tap to your interceptor will trigger when a plugin taps into a hook. Provided is the Tap object. Tap object can't be changed.

loop: (...args) => void Adding loop to your interceptor will trigger for each loop of a looping hook.

register: (tap: Tap) => Tap | undefined Adding register to your interceptor will trigger for each added Tap and allows to modify it.

Context

Plugins and interceptors can opt-in to access an optional context object, which can be used to pass arbitrary values to subsequent plugins and interceptors.

1myCar.hooks.accelerate.intercept({
2	context: true,
3	tap: (context, tapInfo) => {
4		// tapInfo = { type: "sync", name: "NoisePlugin", fn: ... }
5		console.log(`${tapInfo.name} is doing it's job`);
6
7		// `context` starts as an empty object if at least one plugin uses `context: true`.
8		// If no plugins use `context: true`, then `context` is undefined.
9		if (context) {
10			// Arbitrary properties can be added to `context`, which plugins can then access.
11			context.hasMuffler = true;
12		}
13	}
14});
15
16myCar.hooks.accelerate.tap({
17	name: "NoisePlugin",
18	context: true
19}, (context, newSpeed) => {
20	if (context && context.hasMuffler) {
21		console.log("Silence...");
22	} else {
23		console.log("Vroom!");
24	}
25});

HookMap

A HookMap is a helper class for a Map with Hooks

1const keyedHook = new HookMap(key => new SyncHook(["arg"]))

1keyedHook.for("some-key").tap("MyPlugin", (arg) => { /* ... */ });
2keyedHook.for("some-key").tapAsync("MyPlugin", (arg, callback) => { /* ... */ });
3keyedHook.for("some-key").tapPromise("MyPlugin", (arg) => { /* ... */ });

1const hook = keyedHook.get("some-key");
2if(hook !== undefined) {
3	hook.callAsync("arg", err => { /* ... */ });
4}

Hook/HookMap interface

Public:

1interface Hook {
2	tap: (name: string | Tap, fn: (context?, ...args) => Result) => void,
3	tapAsync: (name: string | Tap, fn: (context?, ...args, callback: (err, result: Result) => void) => void) => void,
4	tapPromise: (name: string | Tap, fn: (context?, ...args) => Promise<Result>) => void,
5	intercept: (interceptor: HookInterceptor) => void
6}
7
8interface HookInterceptor {
9	call: (context?, ...args) => void,
10	loop: (context?, ...args) => void,
11	tap: (context?, tap: Tap) => void,
12	register: (tap: Tap) => Tap,
13	context: boolean
14}
15
16interface HookMap {
17	for: (key: any) => Hook,
18	intercept: (interceptor: HookMapInterceptor) => void
19}
20
21interface HookMapInterceptor {
22	factory: (key: any, hook: Hook) => Hook
23}
24
25interface Tap {
26	name: string,
27	type: string
28	fn: Function,
29	stage: number,
30	context: boolean,
31	before?: string | Array
32}

Protected (only for the class containing the hook):

1interface Hook {
2	isUsed: () => boolean,
3	call: (...args) => Result,
4	promise: (...args) => Promise<Result>,
5	callAsync: (...args, callback: (err, result: Result) => void) => void,
6}
7
8interface HookMap {
9	get: (key: any) => Hook | undefined,
10	for: (key: any) => Hook
11}

MultiHook

A helper Hook-like class to redirect taps to multiple other hooks:

1const { MultiHook } = require("tapable");
2
3this.hooks.allHooks = new MultiHook([this.hooks.hookA, this.hooks.hookB]);