I want to rename file name to the expected output. The problem is some user has upload file name with special characters that I cant put on replace statement. If using replace(/\W/g, '') it will remove extension "."

My requirement is :

1. replace space into "_"
2. only allow alphanumeric characters, remove all special characters include "."
3. maintain file .extension

Example :

var file_name = "6$.6j& Fh*^h�