Partial matching a string against a regex

Sassan Haradji sassanh at
Fri Mar 3 21:16:32 UTC 2017

Suppose that I have this regular expression: /abcd/ Suppose that I want to check the user input against that regex and disallow entering invalid characters in the input. When user inputs "ab", it fails as an match for the regex, but I can't disallow entering "a" and then "b" as user can't enter all 4 characters at once (except for copy/paste). So what I need here is a partial match which checks if an incomplete string can be potentially a match for a regex.

Java has something for this purpose: .hitEnd() (described here python doesn't do it natively but has this package that does the job:

I didn't find any solution for it in js. It's been asked years ago: and even before that:
And I asked it here again: and still no answer.

I’ve created an issue requesting this feature on xregexp. But I think it’d be great if native js regex engine could handle this it.

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