Feathers Hooks

Feathers Hooks

Hooks are just small middleware functions that get applied before and after a service method executes. The concept comes from Aspect Oriented Programming and they are construct for implementing Cross Cutting Concerns.

A hook is transport independent, which means it does not matter if it has been called through HTTP(S) (REST), Socket.io, Primus or any other transport Feathers may support in the future.

They are also service agnostic, meaning they can be used with ​any​ service regardless of whether they have a model or not. This keeps services lighter weight and only focused on the CRUD part of an application. An added benefit of not having things like validation baked into your services is flexibility.

Using hooks allows you to easily decouple the actual service logic from things like authorization, data pre-processing (sanitizing and validating), data post processing (serialization), or sending notifications like emails or text messages after something happened.

That way you can swap databases or ORMs with minimal application code changes. You can also share validations for multiple databases in the same app, across multiple apps, and with your client. If hooks weren't completely independent of the service this would be extremely difficult to accomplish.

If you would like to learn more about the design patterns behind hooks read up on API service composition with hooks. In this chapter we will look at the usage of hooks and some commonly used hooks.

Quick Start

To get a high level view of using hooks, see the example below. To learn more about the different ways you can register hooks view the Usage section.

To install from NPM run:

$ npm install feathers-hooks

Then, to use the plugin in a Feathers app:

const feathers = require('feathers');
const hooks = require('feathers-hooks');

const app = feathers().configure(hooks());

Now we can register a hook for a service:

const service = require('feathers-memory');

// Initialize our service
app.use('/users', service());

// Get our initialized service so that we can bind hooks
const userService = app.service('/users');

const myHook = options => { // always wrap in a function so you can pass options and for consistency.
  return hook => {
    console.log('My custom hook ran');
    return Promise.resolve(hook); // A good convention is to always return a promise.
  };
};

// Set up our before hook
userService.before({
  all: [], // run hooks for all service methods
  find: [myHook()] // run hook on before a find. You can chain multiple hooks.
});

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