Javascript REGEX for Subdomain (Optional)

Question

I am looking for a REGEX (JS) that I can use to match all subdomains for a domain as well as the TLD domain in email addresses.

Here is an example:

I would like to be able to match any the following:

joe@canada.ca
joe@it.canada.ca
joe.smith@business.canada.ca

But not match

joe@visitcanada.ca

By default we use something like:

/(.*)@(.*)canada\.ca/gm

But this matches all of the above. Would ideally like a single REGEX that will accomplish all of this.

Why are you matching an `@`? The current pattern does not match any of the above — The fourth bird, Mar 07 '22 at 20:57
They are email addresses we are checking against. Left that off. sorry — VisualSP - DEV, Mar 07 '22 at 20:59
Like this? `^[^\s@]+@(?:[^\s.]+\.)*canada\.ca$` https://regex101.com/r/etLosM/1 — The fourth bird, Mar 07 '22 at 21:01

The fourth bird · Accepted Answer · 2022-03-07T21:08:32.503

1

You could use

^[^\s@]+@(?:[^\s@.]+\.)*canada\.ca$

^ Start of string
[^\s@]+ Match 1+ chars other than a whitespace char or @
@ Match literally
(?:[^\s@.]+\.)* Match optional repetitions of 1+ chars other than a whitespace char, @ or dot, and then match the .
canada\.ca Match canada.ca (Note to escape the dot to match it literally
$ End of string

Regex 101 demo.

const regex = /^[^\s@]+@(?:[^\s@.]+\.)*canada\.ca$/;
[
  "joe@canada.ca",
  "joe@it.canada.ca",
  "joe.smith@business.canada.ca",
  "joe@visitcanada.ca",
].forEach(s => console.log(`${s} --> ${regex.test(s)}`));

edited Mar 07 '22 at 21:08

answered Mar 07 '22 at 21:06

The fourth bird

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That works. Now I need to use it to learn from. Thank you – VisualSP - DEV Mar 07 '22 at 21:08
1

@VisualSP-DEV This is a pretty good site for [visualizing regexes](https://regexper.com/#%5E%5B%5E%5Cs%40%5D%2B%40%28%3F%3A%5B%5E%5Cs%40.%5D%2B%5C.%29*canada%5C.ca%24) – Gary Mar 07 '22 at 21:12
Thanks, @Gary - I will look at that – VisualSP - DEV Mar 07 '22 at 21:16

score 0 · Answer 2 · answered Mar 07 '22 at 21:10

0

An easier way is to simply anchor canada to a word boundary using \b, that way you can use your regex pretty much word for word:

.*@.*\bcanada\.ca

answered Mar 07 '22 at 21:10

Blindy

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That would allow things like "joe@visit-canada.ca" – Gary Mar 07 '22 at 21:14
@Blindy - thanks, I will look at you solution as well. – VisualSP - DEV Mar 07 '22 at 21:16
Well we're talking about regex here and parsing email addresses. No matter how good you are and how many pages of regex you write, it still won't be RFC-conforming. This is simple and it matches every one of the OP's test cases :) – Blindy Mar 07 '22 at 21:17
I think this falls outside the spirit of the question by matching other valid/simple domains. But I agree with your overall point. – Gary Mar 07 '22 at 21:25

Javascript REGEX for Subdomain (Optional)

2 Answers2