I have a regex, but it's a bit tricky.
^(?:(?<Numbers>[0-9]{1})|(?<Alpha>[a-zA-Z]{1})|(?<Special>[^a-zA-Z0-9]{1})){6,50}$
Let me explain it and how to check if the tested password is correct:
There are three named groups in the regex.
1) "Numbers": will match a single number in the string.
2) "Alpha": will match a single character from "a" to "z" or "A" to "Z"
3) "Special": will match a single character not being "Alpha" or "Numbers"
Those three named groups are grouped in an alternative group, and {6,50}
advises regex machine to capture at least 6 of those groups mentiond above, but not more than 50.
To ensure a correct password is entered you have to check if there is a match, and after that, if the matched groups are capture as much as you desired. I'm a C# developer and don't know, how it works in javascript, but in C# you would have to check:
match.Groups["Numbers"].Captures.Count > 1
Hopefully it works the same in javascript! Good luck!