JavaScript getKeyList

getKeyList.js

/*
use like so:

let keyList = getKeyList("a", "b", "c")
console.log(keyList[0]) // "a"
console.log(keyList.index["a"]) // 0
*/

function getKeyList() {
  let arr = [].slice.call(arguments);
  arr.index = {};
  arr.forEach((key, i) => {
    arr.index[key] = i;
  })
  return arr;
}