Negative array using Proxy

negative_array.js

function negArray (arr) {
  return Proxy.create({
    get: function (rcvr, index) {
      index = +index;
      return arr[index < 0? arr.length + index : index];
    },

    set: function (rcvr, index, value) {
      index = +index;
      return arr[index < 0? arr.length + index : index] = value;
    }
  })
}