ProxyFrozen.js

'use strict'

class Frozen {
  constructor() {
    Object.freeze(this);
  }
  bar(...args) {
    console.log('bar', ...args);
  }
}

let f = new Frozen();
f.bar('no proxy');
// prints "bar no proxy"

try {
  // With 'use strict', this throws an error
  f.bar = () => {
    console.log('bar2')
  }
} catch (e) {
  console.log('Cannot extend');
  // prints "Cannot extend"
}

f = new Proxy(f, {
  // Called on f.bar (before function execution)
  get: (target, prop) => {
    // Select the properties you want to proxy
    if (prop !== 'bar') {
      return target[prop];
    }
    return (...args) => {
      console.log('CALLING', prop, ...args)
      // prints "CALLING bar with proxy 12 false"
      target[prop].call(target, ...args)
    }
  }
})

f.bar('with proxy', 12, false);
// prints "bar with proxy 12 false"