Also, note that you have to assign the result of the .replace() to a variable because it returns a new string. It does not modify the existing string. Strings in Javascript are immutable (they aren't directly modified) so any modification operation on a string like .slice(), .concat(), .replace(), etc... returns a new string.
let words = "a\nb\nc\nd\ne";
console.log("Before:");
console.log(words);
words = words.replace(/\n/g, " ");
console.log("After:");
console.log(words);