How to replace the last four digits if such a match occurs?

Question

JavaScript

There is such a line: I cannot solve the following problem: If there are four zeros at the end of the string, then you need to reduce them (replace, probably) to two.
var $time = '21:32:13.210000';

Answer 1

$time.replace(/0{4}$/, '00')

Answer 2

$time.split(".")[0]+"."+$time.split(".")[1].replace(/0{4}$/, '00')