readme.md

@feathersjs/hooks

@feathersjs/hooks brings Koa style asynchronous middleware to any asynchronous JavaScript or TypeScript function.

Installation

npm install @feathersjs/hooks --save

Quick Example

The following example logs the runtime of a function:

const hooks = require('@feathersjs/hooks');
const logRuntime = async (ctx, next) => {
  const start = new Date().getTime();

  await next();

  const end = new Date().getTime();

  console.log(`Function call took ${end - start}ms`);
}

const sayHello = hooks(async message => {
  return `Hello ${message}!`;
}, [ logRuntime ]);

console.log(await sayHello('David'));

Documentation

Hook functions

Hook functions take a context ctx and an asynchronous next function as their argument. The control flow is the exact same as in KoaJS. A hook function can do things before calling await next() and after all other hooks and the function call returned:

const hooks = require('@feathersjs/hooks');

const sayHello = async message => {
  return `Hello ${message}!`;
};

const logMethod = async (ctx, next) => {
  console.log('Before calling method');
  console.log('Arguments are', ctx.arguments);

  await next();

  console.log('Method called');
  console.log('Result is', ctx.result);
}

const hookedSayHello = hooks(sayHello, [ logMethod ]);

Context

• ctx.arguments - The arguments of the function as an array
• ctx.method - The name of the function (if it belongs to an object)
• ctx.this - The this context of the function being called

Decorators

Hooks can also be attached through ES expiremental or TypeScript decorators:

import hooks from '@feathersjs/hooks';

class App {
  @hooks([ logMethod ])
  async sayHi (name) {
    return `Hello ${name}`;
  }
}

More Examples

Cache results

The following example is a simple hook that caches the results of a function call and uses the cached value if available. This is useful e.g. for external Ajax requests:

const hooks = require('@feathersjs/hooks');
const cache = () => {
  const cacheData = {};
  
  return async (ctx, next) => {
    const key = JSON.stringify(ctx);

    if (cacheData[key]) {
      ctx.result = cacheData[key];

      return next();
    }

    await next();

    cacheData[key] = ctx.result;
  }
}

const getData = hooks(async url => {
  return axios.get(url);
}, [ cache() ]);

await getData('http://url-that-takes-long-to-respond');

Decorators

import hooks from '@feathersjs/hooks';

class Api {
  @hooks([
    logRuntime,
    cache()
  ])
  async getMessages () {
    const { data } = axios.get('http://myserver.com/users');

    return data;
  }
}

License

Copyright (c) 2020

Licensed under the MIT license.