//Reverse the Case
function reverseCase(str) {
    return str.replace(/./g, c => c === c.toUpperCase() ? c.toLowerCase() : c.toUpperCase());
}
console.log(reverseCase("Happy Birthday"));    // "hAPPY bIRTHDAY"
console.log(reverseCase("MANY THANKS"));    // "many thanks"
console.log(reverseCase("sPoNtAnEoUs"));    // "SpOnTaNeOuS"