javascript regex for extracting filename from Content-Disposition header

You could try something in this spirit:

filename[^;=\n]*=((['"]).*?\2|[^;\n]*)

filename      # match filename, followed by
[^;=\n]*      # anything but a ;, a = or a newline
=
(             # first capturing group
    (['"])    # either single or double quote, put it in capturing group 2
    .*?       # anything up until the first...
    \2        # matching quote (single if we found single, double if we find double)
|             # OR
    [^;\n]*   # anything but a ; or a newline
)

Your filename is in the first capturing group: http://regex101.com/r/hJ7tS6

Slightly modified to match my use case (strips all quotes and UTF tags)

filename\*?=['"]?(?:UTF-\d['"]*)?([^;\r\n"']*)['"]?;?

https://regex101.com/r/UhCzyI/3