Infinite default dictionary in Javascript ES6

from-py.js

function handlerMaker(obj) {
  return {
   getOwnPropertyDescriptor: function(name) {
     var desc = Object.getOwnPropertyDescriptor(obj, name);
     // a trapping proxy's properties must always be configurable
     if (desc !== undefined) { desc.configurable = true; }
     return desc;
   },
   getPropertyDescriptor:  function(name) {
     var desc = Object.getPropertyDescriptor(obj, name); // not in ES5
     // a trapping proxy's properties must always be configurable
     if (desc !== undefined) { desc.configurable = true; }
     return desc;
   },
   getOwnPropertyNames: function() {
     return Object.getOwnPropertyNames(obj);
   },
   getPropertyNames: function() {
     return Object.getPropertyNames(obj);                // not in ES5
   },
   defineProperty: function(name, desc) {
     Object.defineProperty(obj, name, desc);
   },
   delete:       function(name) { return delete obj[name]; },
   fix:          function() {
     if (Object.isFrozen(obj)) {
       var result = {};
       Object.getOwnPropertyNames(obj).forEach(function(name) {
         result[name] = Object.getOwnPropertyDescriptor(obj, name);
       });
       return result;
     }
     // As long as obj is not frozen, the proxy won't allow itself to be fixed
     return undefined; // will cause a TypeError to be thrown
   },

   has:          function(name) { return name in obj; },
   hasOwn:       function(name) { return ({}).hasOwnProperty.call(obj, name); },
   get:          function(receiver, name) { return obj[name]; },
   set:          function(receiver, name, val) { obj[name] = val; return true; }, // bad behavior when set fails in non-strict mode
   enumerate:    function() {
     var result = [];
     for (var name in obj) { result.push(name); };
     return result;
   },
   keys: function() { return Object.keys(obj); }

  };
}

function defaultDict(fn) {
    var innerObj = {};
    var handler = handlerMaker(innerObj);
    handler.get = function(recv, key) {
        console.log('get ' + key);
        return key in innerObj ? innerObj[key] : (innerObj[key] = fn());
    };
    handler.set = function(recv, key, value) {
        console.log('set ' + key);
        innerObj[key] = value;
    }
    return Proxy.create(handler);
}

function infinite() {
    return defaultDict(infinite)
}

var y = infinite()
console.log(y.a.b.c.d = 1)