Partial matching a string against a regex

Question

Suppose that I have this regular expression: /abcd/ Suppose that I wanna check the user input against that regex and disallow entering invalid characters in the input. When user

Answer 1

This is the hard solution for those who think there's no solution at all: implement the python version (https://bitbucket.org/mrabarnett/mrab-regex/src/4600a157989dc1671e4415ebe57aac53cfda2d8a/regex_3/regex/_regex.c?at=default&fileviewer=file-view-default) in js. So it is possible. If someone has simpler answer he'll win the bounty.

Example using python module (regular expression with back reference):

$ pip install regex
$ python
>>> import regex
>>> regex.Regex(r'^(\w+)\s+\1$').fullmatch('abcd ab',partial=True)