How to add back-access syntax to JS Arrays and strings

0.md

This allows you to use back-access syntax to access items in an array or characters in a string.

In practical terms, it adds the negative integer in arr[-1] to the length of the array/string and tries to search for that property inside the object.

Examples

const arr = backAccess(['first', 'second', 'last'])
arr[-1] // => "last"
arr[-2] // => "second"
arr[-3] // => "first"

const str = backAccess('Hello world!')
str[-1] // => "!"
str[-2] // => "d"
str[-3] // => "l"

Conclusion

Proxies are awesome! But maybe a bit useless in practical terms xD

backaccess.js

module.exports = function backAccess (arg) {
  return new Proxy(typeof arg === 'string' ? new String(arg) : arg, {
    get: (obj, prop, receiver) => {
      try {
        let key = parseInt(prop)

        return Reflect.get(obj, key < 0 ? obj.length + key : key, receiver)
      } catch (e) {
        return Reflect.get(obj, prop, receiver)
      }
    }
  })
}