# Tapable
The tapable package expose many Hook classes, which can be used to create hooks for plugins.
``` javascript
const {
SyncHook,
SyncBailHook,
SyncWaterfallHook,
SyncLoopHook,
AsyncParallelHook,
AsyncParallelBailHook,
AsyncSeriesHook,
AsyncSeriesBailHook,
AsyncSeriesWaterfallHook
} = require("tapable");
```
## Installation
``` shell
npm install --save tapable
```
## Usage
All Hook constructors take one optional argument, which is a list of argument names as strings.
``` js
const hook = new SyncHook(["arg1", "arg2", "arg3"]);
```
The best practice is to expose all hooks of a class in a `hooks` property:
``` js
class Car {
constructor() {
this.hooks = {
accelerate: new SyncHook(["newSpeed"]),
brake: new SyncHook(),
calculateRoutes: new AsyncParallelHook(["source", "target", "routesList"])
};
}
/* ... */
}
```
Other people can now use these hooks:
``` js
const myCar = new Car();
// Use the tap method to add a consument
myCar.hooks.brake.tap("WarningLampPlugin", () => warningLamp.on());
```
It's required to pass a name to identify the plugin/reason.
You may receive arguments:
``` js
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:
``` js
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:
``` js
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.
## 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__. TODO
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:
``` js
myCar.hooks.calculateRoutes.intercept({
call: (source, target, routesList) => {
console.log("Starting to calculate routes");
},
register: (tapInfo) => {
// tapInfo = { type: "promise", name: "GoogleMapsPlugin", fn: ... }
console.log(`${tapInfo.name} is doing its job`);
return tapInfo; // may return a new tapInfo object
}
})
```
**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.
``` js
myCar.hooks.accelerate.intercept({
context: true,
tap: (context, tapInfo) => {
// tapInfo = { type: "sync", name: "NoisePlugin", fn: ... }
console.log(`${tapInfo.name} is doing it's job`);
// `context` starts as an empty object if at least one plugin uses `context: true`.
// If no plugins use `context: true`, then `context` is undefined.
if (context) {
// Arbitrary properties can be added to `context`, which plugins can then access.
context.hasMuffler = true;
}
}
});
myCar.hooks.accelerate.tap({
name: "NoisePlugin",
context: true
}, (context, newSpeed) => {
if (context && context.hasMuffler) {
console.log("Silence...");
} else {
console.log("Vroom!");
}
});
```
## HookMap
A HookMap is a helper class for a Map with Hooks
``` js
const keyedHook = new HookMap(key => new SyncHook(["arg"]))
```
``` js
keyedHook.tap("some-key", "MyPlugin", (arg) => { /* ... */ });
keyedHook.tapAsync("some-key", "MyPlugin", (arg, callback) => { /* ... */ });
keyedHook.tapPromise("some-key", "MyPlugin", (arg) => { /* ... */ });
```
``` js
const hook = keyedHook.get("some-key");
if(hook !== undefined) {
hook.callAsync("arg", err => { /* ... */ });
}
```
## Hook/HookMap interface
Public:
``` ts
interface Hook {
tap: (name: string | Tap, fn: (context?, ...args) => Result) => void,
tapAsync: (name: string | Tap, fn: (context?, ...args, callback: (err, result: Result) => void) => void) => void,
tapPromise: (name: string | Tap, fn: (context?, ...args) => Promise<Result>) => void,
intercept: (interceptor: HookInterceptor) => void
}
interface HookInterceptor {
call: (context?, ...args) => void,
loop: (context?, ...args) => void,
tap: (context?, tap: Tap) => void,
register: (tap: Tap) => Tap,
context: boolean
}
interface HookMap {
for: (key: any) => Hook,
tap: (key: any, name: string | Tap, fn: (context?, ...args) => Result) => void,
tapAsync: (key: any, name: string | Tap, fn: (context?, ...args, callback: (err, result: Result) => void) => void) => void,
tapPromise: (key: any, name: string | Tap, fn: (context?, ...args) => Promise<Result>) => void,
intercept: (interceptor: HookMapInterceptor) => void
}
interface HookMapInterceptor {
factory: (key: any, hook: Hook) => Hook
}
interface Tap {
name: string,
type: string
fn: Function,
stage: number,
context: boolean
}
```
Protected (only for the class containing the hook):
``` ts
interface Hook {
isUsed: () => boolean,
call: (...args) => Result,
promise: (...args) => Promise<Result>,
callAsync: (...args, callback: (err, result: Result) => void) => void,
}
interface HookMap {
get: (key: any) => Hook | undefined,
for: (key: any) => Hook
}
```
## MultiHook
A helper Hook-like class to redirect taps to multiple other hooks:
``` js
const { MultiHook } = require("tapable");
this.hooks.allHooks = new MultiHook([this.hooks.hookA, this.hooks.hookB]);
```
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