How to add a slash to the end of a line in a regular expression?

Question

Regular Expressions

There is a regular expression that removes duplicate slashes from the path:

const url = 'http://localhost////example///author/admin';
clean_url = url.replace(/([^:]\/)\/+/g, "$1")
console.log(clean_url) // http://localhost/example/author/admin

How to complete it so that it adds a slash at the end of the line if it is not there?
For example:

Bad: http://localhost/example/author/admin
Good: http://localhost/example/author/admin/

Bad: http://localhost/example/author/admin?query=1212
Good: http://localhost/example/author/admin/?query=1212

Answer 1

clean_url = url.replace(/($|\?)/, "/$1").replace(/([^:]\/)\/+/g, "$1")