What's the best way (most efficient) to turn all the keys of an object to lower case?

Question

I\'ve come up with

function keysToLowerCase (obj) {
  var keys = Object.keys(obj);
  var n = keys.length;
  while (n--) {
    var key = keys[n]; // \"cache\"         


        

Answer 1

ES6 version:

Object.keys(source)
  .reduce((destination, key) => {
    destination[key.toLowerCase()] = source[key];
    return destination;
  }, {});