Extremely Simple Hooks

Asynchronous hooks for NodeJS and browsers. Works with promise-based architectures.

Installing

npm install eshooks

Using

Hooks registered using the on() method and return Promises. If it returns a Promise, the hook finishes executing before the next hook starts.

import HooksStorage from 'eshooks'

const hooks = new HooksStorage()

hooks.on('start', (...args) => console.log(`Pre-start check - stage 0: ${JSON.stringify(args)}`))
hooks.on('start', (...args) => console.log(`Pre-start check - stage 1: ${JSON.stringify(args)}`))

hooks.trigger('start', 'test').then(() => console.log('Starting...'))

Output:

Pre-start check - stage 0: ["test"]
Pre-start check - stage 1: ["test"]
Starting...

Priorities

Priorities can be specified as a second argument to .on(). Lower priorities execute first. If no priority is specified, it defaults to 0. If multiple hooks are registered with the same priority, they are executed in the order they are registered.

import HooksStorage from 'eshooks'

const hooks = new HooksStorage()

hooks.on('start', (...args) => console.log(`Pre-start check - stage 0: ${JSON.stringify(args)}`))
hooks.on('start', 2, (...args) => console.log(`Pre-start check - stage 2: ${JSON.stringify(args)}`))
hooks.on('start', 1, (...args) => console.log(`Pre-start check - stage 1: ${JSON.stringify(args)}`))
hooks.on('start', 2, (...args) => console.log(`Pre-start check - stage 3: ${JSON.stringify(args)}`))

hooks.trigger('start', 'test').then(() => console.log('Starting...'))

Output:

Pre-start check - stage 0: ["test"]
Pre-start check - stage 1: ["test"]
Pre-start check - stage 2: ["test"]
Pre-start check - stage 3: ["test"]
Starting...

Errors

You can also register an error cleanup function with registering a hook. This function should undo any effects of the hook that need to be undone on error. If an error occurs in the chain of hooks, the error cleanup function of any previous hooks (not including the hook that generated the error) are called in reverse order.

import HooksStorage from 'eshooks'

const hooks = new HooksStorage()

hooks.on('start', (...args) => console.log('Pre-start check - stage 0'),
                  (err, ...args) => console.log('Reverting stage 0'))
                  
hooks.on('start', (...args) => console.log('Pre-start check - stage 1'), 
                  (err, ...args) => console.log('Reverting stage 1'))
                  
hooks.on('start', (...args) => { console.log('Pre-start check - stage 1'); throw new Error(args) },
                  (err, ...args) => console.log('Reverting stage 2'))
                  
hooks.on('start', (...args) => console.log('Pre-start check - stage 3'),
                  (err, ...args) => console.log('Reverting stage 3'))

hooks.trigger('start', 'test')
     .then(() => console.log('Starting...'), (err) => console.log('Aborting...', err))

Output:

Pre-start check - stage 0
Pre-start check - stage 1
Reverting stage 1
Reverting stage 0
Aborting... Error 'test'