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4.4.2 • Public • Published


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Lightweight, solid, framework agnostic and easy to use library which provides reflection features to deal with Cross Cutting Concerns and improve modularity in your code.

Try it!

Clone the repo: git clone

Run showcase: node showcase.js

Run tests: npm test

Features, from bottom to top.

  • ES6 class alternative
  • Inheritance
  • Composition
  • Method Overriding
  • Dependency Injection
  • AOP Extensions

Get started

npm install kaop --save
import { extend } from 'kaop'
// Array.prototype.includes() polyfill
const MyArray = extend(Array, {
  includes(value) {
    return this.indexOf(value) > -1;
const arr = new MyArray(1, 2, 3, 4);
arr.includes(2); // true
arr.includes(5); // false

Easy, right? lets try something else.

Say that for calculating John Doe's age we have to waste a lot of resources so we want to apply memoization to one method.

// create a spy function
const methodSpy = jest.fn();
const Person = createClass({
  constructor(name, yearBorn) { = name;
    this.age = new Date(yearBorn, 1, 1);
  // note that `sayHello` always calls `veryHeavyCalculation`
  veryHeavyCalculation: [, function() {
      // call spy function
      const today = new Date();
      return today.getFullYear() - this.age.getFullYear();
  }, Memoize.write],
    return `hello, I'm ${}, and I'm ${this.veryHeavyCalculation()} years old`;
// ... test it
it("cache advices should avoid 'veryHeavyCalculation' to be called more than once", () => {
  const personInstance = new Person("John Doe", 1990);
// we're creating a group of advices which provides memoization
const Memoize = (function() {
  const CACHE_KEY = "#CACHE";
  return {
    read: reflect.advice(meta => {
      if(!meta.scope[CACHE_KEY]) meta.scope[CACHE_KEY] = {};
      if(meta.scope[CACHE_KEY][meta.key]) {
        meta.result = meta.scope[CACHE_KEY][meta.key];
    write: reflect.advice(meta => {
      meta.scope[CACHE_KEY][meta.key] = meta.result;

O_O what are advices?

Advices are pieces of code that can be plugged in several places within OOP paradigm like 'beforeMethod', 'afterInstance'.. etc. Advices are used to change, extend, modify the behavior of methods and constructors non-invasively.

If you're looking for better experience using advices and vanilla ES6 classes you should check kaop-ts which has a nicer look with ES7 Decorators.

But this library isn't only about Advices right?

This library tries to provide an alternative to ES6 class constructors which can be nicer in some way but do not allow reflection (it seems that ES7 Decorators are the way to go but they're still experimental) compared to createClass prototyping shell which provides a nice interface to put pieces of code that allows declarative Inversion of Control.

Once you have reflection...

Building Dependency Injection system is trivial. For example:

import { createClass, inject, provider } from 'kaop'
// having the following service
const Storage = createClass({
  constructor: function() { = {};
  get: function(key){
  set: function(key, val){
    return[key] = val;
// you declare a singleton provider (you can use a factory for multiple instances)
const StorageProvider = provider.singleton(Storage);
// and then you inject it in several classes
const Model1 = createClass({
  constructor: [inject.args(StorageProvider), function(_storageInstance) { = _storageInstance;
const Model2 = createClass({
  constructor: [inject.args(StorageProvider), function(_storageInstance) { = _storageInstance;
const m1 = new Model1;
const m2 = new Model2; instanceof Storage // true instanceof Storage // true
// and they are the same instance coz `StorageProvider` returns a single instance `singleton`


Way more documentation about Aspect Oriented, Dependency Injection, Composition, Asynchronous Advices, etc.

Tests are the most useful documentation nowadays, that should change soon.

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