Trapping class definition via Proxy in ES6

Question

Is it possible to trap extends? Or to trap definitions inside a class? Eg:

class B extends A {
    method1( ) { }
    static method2( ) { }
}

Is there any way to trap the events that:

• B extended A.
• method1( ) was defined on B.prototype
• method2( ) was defined on B.

None of the existing mechanisms seem to work. Tried setPrototypeOf and defineProperty traps.

Answer 1

When class B extends class A, it gets its prototype object. So you can define a Proxy with a trap on get et check if the property being accessed is "prototype".

class A {}

PA = new Proxy(A, {
  get(target, property, receiver) {
    console.log('get', property)
    if (property == 'prototype')
      console.info('extending %o, prototype=%s', target, target.prototype)
    return target[property]
  }
})

class B extends PA {}