An ES6 proxy making use of "double-lifting" (i.e. a proxy whose handler is a proxy). Allows you to write generic handlers that only have to implement a single trap, yet can intercept all possible operations.

doublelifting.js

// a proxy making use of "double-lifting" (i.e. a proxy whose handler is a proxy)

var metaHandler = {
  get: function(dummyTarget, trapName, dummyReceiver) {
    return function(...trapArgs) { // function acting as a generic trap, its this-binding is irrelevant
      console.log("intercepting "+trapName);
      return Reflect[trapName](...trapArgs); // forward manually
    }
  },
};

var target = {x:1};
var dummy = {};
var doubleLiftedProxy = new Proxy(target, new Proxy(dummy, metaHandler));

doubleLiftedProxy.x // intercepting get, evals to 1
'x' in doubleLiftedProxy // interecepting has, evals to true