Swapping first letters in name and altering capitalization using JavaScript? (looking to optimize solution)

I was taking on a JS challenge to take a first/last name string input and do the following:

1. swap the first letter of first/last name
2. convert all characters to lowercase, except for the first characters, which need to be uppercase

Example: input: DonAlD tRuMp
output: Tonald Drump

The following is the code I came up with:

const input = prompt("Enter a name:")

function switchFirstLetters(input) {
    let stringArray = input.split('');

    for(let i=0; i < stringArray.length; i++) {
        if(stringArray[i - 1] === ' ') {
            [stringArray[0], stringArray[i]] = [stringArray[i], stringArray[0]]; // destructuring
        }
    }

    return result = stringArray.join('');
}

let swappedString = switchFirstLetters(input);

function capFirstLetters(swappedString) {
    let stringArray = swappedString.toLowerCase();
    stringArray = stringArray.split('');
    stringArray[0] = stringArray[0].toUpperCase();

    for(let i=0; i < stringArray.length; i++) {
        if(stringArray[i - 1] === ' ') {
            stringArray[i] = stringArray[i].toUpperCase();
        }
    }

    return result = stringArray.join('');
}

let finalString = capFirstLetters(swappedString);
console.log(finalString);

My thought process for the switchFirstLetters function was:

1. Create an array from the string parameter
2. Run through the array length. If the value of the element prior the current element is equal to ' ', use destructuring to swap the current element with the element at index 0
3. Concatenate elements into a new string and return that value

My thought process for the capFirstLetters function:

1. Convert all characters in the string to lowercase (this could be handled outside of the function as well)
2. Create an array from the new, lowercase string
3. Make character at index 0 be uppercase (this could also be integrated into the for loop)
4. Run through the array length. If the value of the element prior to the current element is equal to ' ', convert that element to uppercase.
5. Concatenate array elements into a new string

The code works, but I'm still early in my coding journey and realize it's likely not an ideal solution, so I was wondering if anyone here could help me optimize this further to help me learn. Thanks!

You could also use a regular expression to replace the first letters:

let name = "DonAlD tRuMp";

let result = name.toLowerCase().replace(/(\S)(\S*\s+)(\S)/g, (_, a, b, c) =>
    c.toUpperCase() + b + a.toUpperCase()
);

console.log(result);

The regular expression uses \S (a non-white-space character), \S* (zero or more of those), \s+ (one or more white-space characters) and parentheses to create capture groups. These three groups map to a,b,c parameters in the callback function that is passed to replace as second argument. With these parts the replacement string can be constructed. Both the capitalisation and the switch happen in the construction.