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

Using Object.fromEntries (ES10)

Native and immutable solution using the new Object.fromEntries method:

const newObj = Object.fromEntries(
  Object.entries(obj).map(([k, v]) => [k.toLowerCase(), v])
);

Until that function becomes widely available you could define it yourself with the following polyfill:

Object.fromEntries = arr => Object.assign({}, ...Array.from(arr, ([k, v]) => ({[k]: v}) ));

A nice thing is that this method does the opposite of Object.entries, so now you can go back and forth between the object and array representation.