JS proxied class definitions

proxied-class-definition.js

/*
   You can safely wrap a class definition in a Proxy.
   Note that the class instance will not be a Proxy. To do that, this pattern can be used:
   const handler = {...};
   class Foo {
     constructor () {
       return new Proxy(this, handler);
     }
   }
 */

class Foo {
  constructor () {
    this.foo = 'foo';
  }
  fooMethod () {
    console.log(`I'm a method of Foo.`);
  }
}

function wrap (classToWrap) {
  return new Proxy(classToWrap, {
    get (target, property, receiver) {
      console.log(`Getting property “${property}” from ${target.prototype.constructor.name}.`);
      return Reflect.get(...arguments);
    },
    construct (target, args) {
      console.log(`${target.prototype.constructor.name} constructor called`);
      return new target(...args); // or Reflect.construct(target, args);
    },
  });
}

class Test extends wrap(Foo) {
  constructor () {
    super();
    console.log(`I extended a class wrapped in a Proxy!`);
    this.fooMethod();
  }
}

const test = new Test();
console.log(`test instanceof Foo:`, test instanceof Foo);