The tapable package exposes many Hook classes, which can be used to create hooks for plugins.
const{SyncHook,SyncBailHook,SyncWaterfallHook,SyncLoopHook,AsyncParallelHook,AsyncParallelBailHook,AsyncSeriesHook,AsyncSeriesBailHook,AsyncSeriesWaterfallHook}=require("tapable");npm install --save tapable
All Hook constructors take one optional argument, which is a list of argument names as strings.
consthook=newSyncHook(["arg1","arg2","arg3"]);
The best practice is to expose all hooks of a class in ahooks property:
classCar{constructor(){this.hooks={accelerate:newSyncHook(["newSpeed"]),brake:newSyncHook(),calculateRoutes:newAsyncParallelHook(["source","target","routesList"])};}/* ... */}Other people can now use these hooks:
constmyCar=newCar();// Use the tap method to add a consumentmyCar.hooks.brake.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 promisegoogle.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)returncallback(err);routesList.add(route);// call the callbackcallback();});});// You can still use sync pluginsmyCar.hooks.calculateRoutes.tap("CachedRoutesPlugin",(source,target,routesList)=>{constcachedRoute=cache.get(source,target);if(cachedRoute)routesList.add(cachedRoute);});The class declaring these hooks needs to call them:
classCar{/** * You won't get returned value from SyncHook or AsyncParallelHook, * to do that, use SyncWaterfallHook and AsyncSeriesWaterfallHook respectively */setSpeed(newSpeed){// following call returns undefined even when you returned valuesthis.hooks.accelerate.call(newSpeed);}useNavigationSystemPromise(source,target){constroutesList=newList();returnthis.hooks.calculateRoutes.promise(source,target,routesList).then((res)=>// res is undefined for AsyncParallelHookroutesList.getRoutes());}useNavigationSystemAsync(source,target,callback){constroutesList=newList();this.hooks.calculateRoutes.callAsync(source,target,routesList,(err)=>{if(err)returncallback(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.
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 (usingmyHook.tap()).
AsyncSeries. An async-series hook can be tapped with synchronous, callback-based and promise-based functions (usingmyHook.tap(),myHook.tapAsync() andmyHook.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 (usingmyHook.tap(),myHook.tapAsync() andmyHook.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.
All Hooks offer an additional interception API:
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`);returntapInfo;// may return a new tapInfo object}});call:(...args) => void Addingcall to your interceptor will trigger when hooks are triggered. You have access to the hooks arguments.
tap:(tap: Tap) => void Addingtap to your interceptor will trigger when a plugin taps into a hook. Provided is theTap object.Tap object can't be changed.
loop:(...args) => void Addingloop to your interceptor will trigger for each loop of a looping hook.
register:(tap: Tap) => Tap | undefined Addingregister to your interceptor will trigger for each addedTap and allows to modify it.
Plugins and interceptors can opt-in to access an optionalcontext object, which can be used to pass arbitrary values to subsequent plugins and interceptors.
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!");}});A HookMap is a helper class for a Map with Hooks
constkeyedHook=newHookMap((key)=>newSyncHook(["arg"]));
keyedHook.for("some-key").tap("MyPlugin",(arg)=>{/* ... */});keyedHook.for("some-key").tapAsync("MyPlugin",(arg,callback)=>{/* ... */});keyedHook.for("some-key").tapPromise("MyPlugin",(arg)=>{/* ... */});consthook=keyedHook.get("some-key");if(hook!==undefined){hook.callAsync("arg",(err)=>{/* ... */});}Public:
interfaceHook{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;}interfaceHookInterceptor{call:(context?, ...args)=>void;loop:(context?, ...args)=>void;tap:(context?,tap:Tap)=>void;register:(tap:Tap)=>Tap;context:boolean;}interfaceHookMap{for:(key:any)=>Hook;intercept:(interceptor:HookMapInterceptor)=>void;}interfaceHookMapInterceptor{factory:(key:any,hook:Hook)=>Hook;}interfaceTap{name:string;type:string;fn:Function;stage:number;context:boolean;before?:string|Array;}Protected (only for the class containing the hook):
interfaceHook{isUsed:()=>boolean;call:(...args)=>Result;promise:(...args)=>Promise<Result>;callAsync:(...args,callback:(err,result:Result)=>void)=>void;}interfaceHookMap{get:(key:any)=>Hook|undefined;for:(key:any)=>Hook;}A helper Hook-like class to redirect taps to multiple other hooks:
const{ MultiHook}=require("tapable");this.hooks.allHooks=newMultiHook([this.hooks.hookA,this.hooks.hookB]);