to-aop

The to-aop module help you with applying Aspect Oriented Programming to JavaScript. It use under the hood ES Proxy for object same as other similar modules. It allow you hook class without creating new instance as well. It use javascript prototype for that.

For example I am using it for adding hooks to production code where all debug code is missing. I don't have got access to instance but I have only class constructor. But usage is unlimited.

More articles about AOP:

1. https://blog.mgechev.com/2015/07/29/aspect-oriented-programming-javascript-aop-js/
2. https://hackernoon.com/aspect-oriented-programming-in-javascript-es5-typescript-d751dda576d0

Examples:

1. https://github.com/mjancarik/shallow-with-context/blob/master/src/shallowWithContext.js
2. https://github.com/seznam/ima/blob/master/packages/devtools/src/services/defaultSettings.json

Installation

npm i to-aop --save

Usage

Easy example for native Date.now method.

import { aop, hookName, createHook } from 'to-aop';

const nowHook = createHook(hookName.aroundMethod, 'now', (args) => {
    return 1;
});

aop(Date, nowHook);

Date.now() // returns 1

Other example with more hooks for your defined class.

// a.js
export default class A {
  constructor(variable) {
    this.variable = variable;
  }

  method() {
    return this.variable;
  }

  notHookedMethod() {
    return 'not hook';
  }    
}

Applying AOP to class

You can use it for creating hook to your favorite framework or your own application without modification source code.

import { aop, hookName, createHook, unAop } from 'to-aop';
import A from './a';

const classHookBefore = createHook(
  hookName.beforeMethod,
  /^(method)$/,
  ({ target, object, property, context, args, meta }) => {
    //call your own hook
    meta.startTime = performance.now();
    console.log(
      `Instance of ${target.name} call "${property}"
with arguments ${args && args.length ? args : '[]'}.`
    );
  }
);

const classHookAfter = createHook(
  hookName.afterMethod,
  /^(method)$/,
  ({ target, object, property, context, args, payload, meta }) => {
    //call your own hook
    console.log(
      `Instance of ${target.name} call "${property}"
with arguments ${args && args.length ? args : '[]'}
and return value is "${payload}" took ${performance.now() - meta.startTime}.`
    );
  }
);

const hooks = Object.assign({}, classHookBefore, classHookAfter);

aop(
  A,
  hooks
); // bind hook to class
const a = new A('my hook');

a.method(); // log: 'Instance of A call "method" with arguments [] and return value is "my hook".', returns: 'my hook'
a.notHookedClassMethod(); // returns: 'not hook'

unAop(A);
a.method(); // returns: 'my hook'
a.notHookedClassMethod(); // returns: 'not hook'

Applying AOP to instance or object

import { aop, hookName, createHook, unAop } from 'to-aop';
import A from './a';

const instanceHook = createHook(
  hookName.afterMethod,
  /^(method)$/,
  ({ target, object, property, context, args, payload, meta }) => {
    console.log(
      `Instance of ${object.constructor.name} call "${property}"
with arguments ${args && args.length ? args : '[]'}
and return value is "${payload}".`
    );
  }
);

const a = new A('my hook');
const hookedInstance = aop(a, instanceHook); // bind hook to instance

hookedInstance.method(); // log: 'Instance of A call "method" with arguments [] and return value is "my hook.', returns: 'my hook'
hookedInstance.notHookedClassMethod(); // returns: 'not hook'

unAop(a);
a.method(); // returns: 'my hook'
a.notHookedClassMethod(); // returns: 'not hook'

Documentation

createHook(hookName, regular, callbackHook)

• (string) hookName - set of hooks
• (string, regexp, Array, function) regular - condition for filtering
• (function) callbackHook - your defined action

aop(target, pattern, settings)

• (class, object) - target for hooks
• (Object<string, Array>) - pattern of hooks
• {Object} settings
• {booelan} [settings.constructor=false] - allow hook class constructor

unAop(target)

• (class, object) - target for hooks

Hooks API

We implemented base set of hooks which you can use for AOP.

1. beforeMethod
2. afterMethod
3. aroundMethod
4. beforeGetter
5. afterGetter
6. aroundGetter
7. beforeSetter
8. afterSetter
9. aroundSetter

import { hookName } from 'to-aop';

// hookName.(beforeMethod|afterMethod|...)