How to do AOP with node.js?

Question

I have a little problem doing some AOP with node.js: Let\'s say I have an application in a script called server.js, and I want to monitor its functions.

Here is

Answer 1

To avoid reinventing the wheel, you could use nestjs which is a framework that propose a lot of tools. Among them you'll find interceptors which do what you want (i think).

https://nestjs.com/

Answer 2

I think it is due to the nature of the Javascript language - implies a lot of code intrusion.

please don't :'(

AOP is an extension of OOP, there is no AOP without OOP.

I suggest you to use kaop or TS version with ES7 decorators kaop-ts

1º: npm install kaop --save

2º: define an advice to monitor your methods:

import { reflect } from "kaop"

const Log = reflect.advice(meta => {
  //meta.args contains the arguments {array}
   console.log(meta.methodName + " called");
   console.log("with arguments: " + meta.args);
   console.log("returned: " + meta.result);
})

3º you have to organize your code following OOP guidelines:

const Controller = createClass({
  constructor: function(app){
    app.get('/', this.home);
    app.get('/login', this.login);
    app.use(this.notFound);
  },
  login: [function(req, res){
    //what ever
  }, Log],
  home: [function(req, res){
    res.setHeader('Content-Type', 'text/plain');
    res.end('Home');
  }, Log],
  notFound: [function(req, res){
    res.setHeader('Content-Type', 'text/plain');
    res.send(404, 'Page introuvable !');
  }, Log]
})

I've writed an article on 2018 which discuss AOP on JS server side.

Answer 3

A naive attempt would look something like this.

var before = function(object, functionName, action) {
  var oldFunction = object.functionName;
  var newFunction = function() {
    action();
    oldFunction();
  };
  object.functionName = oldFunction;
}

var after = function(object, functionName, action) {
  var fn = object.functionName;
  var after = function() {
    fn();
    action();
  };
  object.functionName = oldFunction;
}

JS is very flexible; you could easily improve on this by storing the after and before actions and adding/removing them as required, but at the very least this should do what you want (albeit not in a very good manner).