function replaceFirst(input, search, replace) {
const index = input.indexOf(search);
if (index === -1) return input;
return input.substring(0, index) + replace + input.substring(index + search.length);
}
const s = "aa bb cc dd ee cc ff";
const result = replaceFirst(s, "cc", "ZZ");
console.log(result);
/*
run:
aa bb ZZ dd ee cc ff
*/