Negative indices on arrays using ES2015 proxies

es2015-proxies-array-negative-indices.js

function yay(array) {
  return new Proxy(array, {
    get (target, property, receiver) {
      if (property < 0) {
        property = target.length + Number(property)
      }
      return Reflect.get(target, property, receiver)
    }
  })
}

// Demo use:

const arr = yay(['foo', 'bar', 'baz'])
arr[-1] // => 'baz'

As a reminder, Babel won't transpile proxies: they can't be emulated in ES5. But you do have enough native support for this, as of May 25 2016, in Edge 12+, Fx38+, Ch49+, Saf TP, and Node 6.