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

For all values:

to_lower_case = function(obj) {
    for (var k in obj){
        if (typeof obj[k] == "object" && obj[k] !== null)
            to_lower_case(obj[k]);
        else if(typeof obj[k] == "string") {
            obj[k] = obj[k].toLowerCase();
        }
    }
    return obj;
}

Same can be used for keys with minor tweaks.

Answer 2

The loDash/fp way, quite nice as its essentially a one liner

import {
mapKeys
} from 'lodash/fp'

export function lowerCaseObjectKeys (value) {
return mapKeys(k => k.toLowerCase(), value)
}

Answer 3

I'd use Lo-Dash.transform like this:

var lowerObj = _.transform(obj, function (result, val, key) {
    result[key.toLowerCase()] = val;
});

Answer 4

Using forEach seems to be a bit quicker in my tests- and the original reference is gone, so deleting the new one will put it in reach of the g.c.

function keysToLowerCase(obj){
    Object.keys(obj).forEach(function (key) {
        var k = key.toLowerCase();

        if (k !== key) {
            obj[k] = obj[key];
            delete obj[key];
        }
    });
    return (obj);
}

var O={ONE:1,two:2,tHree:3,FOUR:4,Five:5,SIX:{a:1,b:2,c:3,D:4,E:5}}; keysToLowerCase(O);

/* returned value: (Object) */

{
    five:5,
    four:4,
    one:1,
    six:{
        a:1,
        b:2,
        c:3,
        D:4,
        E:5
    },
    three:3,
    two:2
}

Answer 5

const keysToLowerCase = object => {
  return Object.keys(object).reduce((acc, key) => {
    let val = object[key];
    if (typeof val === 'object') {
      val = keysToLowerCase(val);
    }
    acc[key.toLowerCase()] = val;
    return acc;
  }, {});
};

Works for nested object.

Answer 6

Simplified Answer

For simple situations, you can use the following example to convert all keys to lower case:

Object.keys(example).forEach(key => {
  const value = example[key];
  delete example[key];
  example[key.toLowerCase()] = value;
});

You can convert all of the keys to upper case using toUpperCase() instead of toLowerCase():

Object.keys(example).forEach(key => {
  const value = example[key];
  delete example[key];
  example[key.toUpperCase()] = value;
});