Hook Middleware Decorators

Add and remove pre, post, and "around" middleware hooks to class methods on a per class instance basis with the help of class and method decorators.

How To Use

import { Hooks, Hook, HookAsync, hasHooks } from 'hook-middleware-decorators'

@Hooks()
class ClassWithHooks {
    @Hook()
    hello(person: string) {
        const message =  `Hello ${person}`;
        console.log(message);
        return message;
    }

    @HookAsync()
    async helloAsync(person: string) {
        const message =   `Hello ${person} async`;
        console.log(message);
        return message;
    }

    noHook(person: string) {
        const message = `No hook called with ${person}`
        console.log(message);
        return message;
    }
}

function preHello(person: string){
    console.log('pre', person)
}

function postHello(message: string, person: string){
    console.log('post', message, person)
}

function aroundHello(func: (person: string)=>string, person: string): string {
  console.log('before hello', person);
  const result = func(person);
  console.log('after hello', result);
  return result;
}

const instance = new ClassWithHooks();
let helloUnsubscriber = () => {}
if(hasHooks<ClassWithHooks>(instance)) { // type-guard to ensure the class is decorated with @Hooks
  helloUnsubscriber = instance.around('hello', aroundHello);
  instance.pre('hello', preHello);
    instance.post('hello', postHello);
    instance.pre('helloAsync', preHello);
    instance.post('helloAsync', postHello);
    instance.pre('noHook', preHello);
    instance.post('noHook', postHello);
}

(async () => {
    instance.hello('world');
    await instance.helloAsync('Earth');
    instance.noHook('stuff')
    helloUnsubscriber();
    instance.hello('Mars');
})();

/**
 * Result:
 *
 * before hello world
 * pre world
 * Hello world
 * post Hello world world
 * after hello Hello world
 * pre Earth
 * Hello Earth async
 * post Hello Earth async Earth
 * No hook called with stuff
 * pre Mars
 * Hello Mars
 * post Hello Mars Mars
 */

Important

The @Hooks class decorator adds pre, post, and around methods to the decorated class. Any methods or properties with the same names in the class definition will be overridden.

If a pre or around function throws an error, the hooked method will throw the error as well. If a post function throws an error, the hooked method will not throw the error.

Registering a pre, post, or around function will result in an unsubscriber being returned. Invoking the unsubscriber will remove the function as a middleware.

Use Cases

1. Put authorization and validation in pre functions
2. Put metrics in around functions where applicable
3. Put any side effects such as notifications in post functions

Best Practices

1. pre, post, and around functions should refrain from mutating any arguments in order to keep behavior predictable.
2. Use the @Hook decorator for synchronous methods. Make sure middleware functions for synchronous methods are also synchronous.
3. Use the @HookAsync decorator for asynchronous methods. pre and post middleware functions for asynchronous methods can be synchronous or asynchronous. around middleware functions must be asynchronous

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