To NameCase

namecase.js

function capitalizeFirstLetter(str) {
    return str.charAt(0).toUpperCase() + str.slice(1);
}

function toNameCase(str) {
    return str.split(" ").map(capitalizeFirstLetter).join(" ")
}

console.log(toNameCase("banana man"))
console.log(toNameCase("ole McDonald"))

namecase_regex.js

/**
 *
 * @param {string} str
 * @returns {*}
 */
function toNameCase(str) {
    return str.replace(/(^|\s)(.)/g, (m) => m.toUpperCase())
}

console.log(toNameCase("banana man"))
console.log(toNameCase("ole McDonald"))

Outputs:

Banana Man
Ole McDonald