Basic es5 proxy

proxy.js

console.clear();

function isFunction(o){
  return typeof o === (typeof isFunction);
}

/**
 * Wraps up an object replacing methods with an interceptor
 * @param obj - the obj to wrap
 * @param interceptor {(obj, methodName, args) => any}
 * @returns the proxy
 */
function createProxy(obj, interceptor){
  var newObj = Object.create(obj);
  var layer = obj;
  var keys = [];
  
  while (layer){
    keys = keys.concat(Object.getOwnPropertyNames(layer));
    layer = Object.getPrototypeOf(layer);
  }
  
  keys.forEach(function(prop){
    if (isFunction(obj[prop])){
      newObj[prop] = function(){
        return interceptor(obj, prop, arguments);
      };
    }
  });

  return newObj;
}

var object = ({
  foo: function(){
    return "bar";
  }
});

var proxy = createProxy(object, function(obj, methodName, args){
  console.log(methodName + " called");
  return obj[methodName].apply(obj, args);
});

console.log( proxy.foo() );