Chuleta de regex para conversión de caso
// Split camelCase into words
"helloWorld".replace(/([a-z])([A-Z])/g, "$1 $2")
// Capitalize first letter of each word
str.replace(/\b\w/g, c => c.toUpperCase())
// Sentence case
str.toLowerCase().replace(/(^\s*\w|[.!?]\s+\w)/g, c => c.toUpperCase())
// Invert case
[...str].map(c => c === c.toUpperCase() ? c.toLowerCase() : c.toUpperCase()).join("")