How can I write a regular expression that matchs case insensitive emails? - regex

Question

I have following code to find user with an email.
User.findOne({
email: { $regex: new RegExp('^' + req.body.email.toLowerCase() + '$','i') }
})
It finds the user with a given email by lowercase letters and case insensitive search.
The problem is, we have some emails like john+doe#johndoe.com and this regular expression doesn't match those emails.
What should I add to regular expression to find that kind of emails?

Answer 1

The issue is that you're using the e-mail address, as req.body.email, unescaped in a regular expression.
As you noticed, characters that have a special meaning in regexes, like +, will cause problems. Even worse, when a user enters .* as their e-mail address, your query will match any user, which is a security concern.
What you want is to escape the e-mail address input so any special characters will be searched for as-is (have their "special meaning" stripped from them).
The easiest way is to use a module like regex-escape that will do that for you:
var escape = require('regex-escape');
...
User.findOne({
email: { $regex: new RegExp('^' + escape(req.body.email) + '$','i') }
})
Since the regex is already set to match case-insensitive, there's not need to lowercase the string.

Answer 2

Description
I use this expression, it's not perfect as there are some edge cases which will slip by but those are easy enough to test by simply sending the test email:
^[_a-z0-9-+]+(?:\.[_a-z0-9-+]+)*#[a-z0-9-]+(?:\.[a-z0-9-]+)*(?:\.[a-z]{2,4})$
By adding A-Z to each of the character classes I've made the same expression case insensitive.
^[_a-zA-Z0-9-+]+(?:\.[_a-zA-Z0-9-+]+)*#[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*(?:\.[a-zA-Z]{2,4})$
Example
Live Demo
https://regex101.com/r/uC5oG4/1
Explanation
NODE EXPLANATION
----------------------------------------------------------------------
^ the beginning of a "line"
----------------------------------------------------------------------
[_a-z0-9-+]+ any character of: '_', 'a' to 'z', '0' to
'9', '-', '+' (1 or more times (matching
the most amount possible))
----------------------------------------------------------------------
(?: group, but do not capture (0 or more times
(matching the most amount possible)):
----------------------------------------------------------------------
\. '.'
----------------------------------------------------------------------
[_a-z0-9-+]+ any character of: '_', 'a' to 'z', '0'
to '9', '-', '+' (1 or more times
(matching the most amount possible))
----------------------------------------------------------------------
)* end of grouping
----------------------------------------------------------------------
# '#'
----------------------------------------------------------------------
[a-z0-9-]+ any character of: 'a' to 'z', '0' to '9',
'-' (1 or more times (matching the most
amount possible))
----------------------------------------------------------------------
(?: group, but do not capture (0 or more times
(matching the most amount possible)):
----------------------------------------------------------------------
\. '.'
----------------------------------------------------------------------
[a-z0-9-]+ any character of: 'a' to 'z', '0' to
'9', '-' (1 or more times (matching the
most amount possible))
----------------------------------------------------------------------
)* end of grouping
----------------------------------------------------------------------
(?: group, but do not capture:
----------------------------------------------------------------------
\. '.'
----------------------------------------------------------------------
[a-z]{2,4} any character of: 'a' to 'z' (between 2
and 4 times (matching the most amount
possible))
----------------------------------------------------------------------
) end of grouping
----------------------------------------------------------------------
$ before an optional \n, and the end of a
"line"
----------------------------------------------------------------------