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

One-liner (only for top level keys):

Object.assign(...Object.keys(obj).map(key => ({[key.toLowerCase()]: obj[key]})))

Converts:

{ a: 1, B: 2, C: { Z: 4 } }

To:

{ a: 1, b: 2, c: { Z: 4 } }