Quick Question about Regular Expression Bracket (JS)

Let's look at what these expressions are saying:

string.replace(/\s\s+/g,' ');

This one says "look for 2 or more spacing characters, and replace them with a single space". \s is one spacing character, \s+ is one or more, so \s\s+ is two or more. This would be a good way to collapse spans of white space.

string.replace(/[\s+]/g,' ');

This says "look for a spacing character or a plus sign, and replace it with a space". The contents of a pair of brackets define a single character, and everything inside is a potential candidate. Inside the brackets, the plus sign loses its meaning of "one or more" and becomes just a plus sign. This would convert tabs and plus signs into spaces (not what you intended).

Since brackets in a regex mean "match any character inside the brackets" [\s+] means match a single whitespace or plus sign character. If you wanted to use + to mean "one or more" it would have to go outside like this [\s]+, but since there is only one character/class the brackets are redundant so it's just \s+