const target = {

  greet: (name) => `Hello ${name}`,

};

​

const decorateIfFunction = (obj) =>

  typeof obj == 'function' ?

    decorateWithLogging(obj) :

    obj;

​

const decorateWithLogging = (fn) => (...args) => {

  console.log(`called ${fn.name} with [${args}]`);

  return fn(...args);

};

​

const proxy = new Proxy(target, {

  get: (target, prop) =>

    decorateIfFunction(target[prop]),

});

​

console.log( proxy.greet('world') );

// Logs "called greet with [world]",

// then "Hello world".