Break Camel Case function in JavaScript

I have been attempting to solve this codewars problem for a while in JavaScript:

"Complete the solution so that the function will break up camel casing, using a space between words. Example:"

"camelCasing"  =>  "camel Casing"

"identifier"   =>  "identifier"

""             =>  ""

I have it almost all the way, but for some reason my code is selecting the wrong space to add a blank space.
I’m hoping someone can tell me what I am doing wrong.

function solution(string) {
  let splitStr = string.split("");
  let newStr = string.split("");
  let capStr = string.toUpperCase().split("");
  for (i = 0; i < splitStr.length; i++) {
    if (splitStr[i] === capStr[i]) {
      newStr.splice(i, 0, ' ');
    }
  }
  return newStr.join("");
}

console.log('camelCasing: ', solution('camelCasing'));
console.log('camelCasingTest: ', solution('camelCasingTest'));

>Solution :

The first insertion into newStr will be at the correct spot, but after that insertion of the space, the letters that follow it in newStr will be at an increased index. This means that when the next capital is found at i in splitStr (which did not change), the insertion into newStr (which did change) should really be at i+1.

A solution is to make your loop iterate from end to start:

function solution(string) {
  let splitStr = string.split("");
  let newStr = string.split("");
  let capStr = string.toUpperCase().split("");
  for (i = splitStr.length - 1; i >= 0; i--) {
    if (splitStr[i] === capStr[i]) {
      newStr.splice(i, 0, ' ');
    }
  }
  return newStr.join("");
}

console.log('camelCasing: ', solution('camelCasing'));
console.log('camelCasingTest: ', solution('camelCasingTest'));

This kind of problem is however much easier solved with a regular expression:

function solution(string) {
  return string.replace(/[A-Z]/g, " $&");
}

console.log('camelCasing: ', solution('camelCasing'));
console.log('camelCasingTest: ', solution('camelCasingTest'));

Explanation of the regular expression:

  • [A-Z] a capital letter from the Latin alphabet.
  • $& backreference to the matched letter, used in the replacement.
  • g global flag so all matches are replaced.

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