Asked  7 Months ago    Answers:  5   Viewed   34 times

I know this question has been asked about a dozen times, but this one is not technically a dupe (check the others if you like) ;)

Basically, I have a Javascript regex that checks email addresses which I use for front-end validation, and I use CodeIgniter to double check on the back end, in case the validation on the front end fails to run properly (browser issues, for instance.) It's QUITE a long regular expression, and I have no idea where to begin converting it by hand.

I'm pretty much looking for a tool that converts JS regexes to PHP regexes - I haven't found one in any of the answers to similar questions (of course, it's possible that such a tool doesn't exist.) Okay, I lied - one of them suggested a tool that costs $39.95, but I really don't want to spend that much to convert a single expression (and no, there isn't a free trial as suggested by the answer to the aforementioned question.)

Here's the Javascript expression, graciously provided by aSeptik:


And the one used by CodeIgniter, which I don't want to use because it doesn't follow the same rules (disallows some valid addresses):


I want to use the same rules set by the Javascript regex in PHP.

Having this sort of inconsistency where my front-end code is saying that the email address is okay, and then Codeigniter says it isn't, is of course the behavior I'm trying to fix in my application.

Thanks for any and all tips! :D



I was able to solve this in a better-than-expected manner. I was unable to convert the Javascript regex that I wanted to use (even after purchasing RegexBuddy - it'll come in handy, but it was not able to produce a proper conversion), so I decided to go looking on the Regex Validate Email Address site to see if they had any recommendations anywhere for good regexes. That's when I found this:

"The expression with the best score is currently the one used by PHP's filter_var()":


It matches with only 4/86 errors, while the Javascript one I was using matches with 8/86 errors, so the PHP one is a little more accurate. So, I extended the CodeIgniter Form_validation library to instead use return filter_var($str, FILTER_VALIDATE_EMAIL);.

...But does it work in Javascript?

var pattern = new RegExp(/^(?!(?:(?:x22?x5C[x00-x7E]x22?)|(?:x22?[^x5Cx22]x22?)){255,})(?!(?:(?:x22?x5C[x00-x7E]x22?)|(?:x22?[^x5Cx22]x22?)){65,}@)(?:(?:[x21x23-x27x2Ax2Bx2Dx2F-x39x3Dx3Fx5E-x7E]+)|(?:x22(?:[x01-x08x0Bx0Cx0E-x1Fx21x23-x5Bx5D-x7F]|(?:x5C[x00-x7F]))*x22))(?:.(?:(?:[x21x23-x27x2Ax2Bx2Dx2F-x39x3Dx3Fx5E-x7E]+)|(?:x22(?:[x01-x08x0Bx0Cx0E-x1Fx21x23-x5Bx5D-x7F]|(?:x5C[x00-x7F]))*x22)))*@(?:(?:(?!.*[^.]{64,})(?:(?:(?:xn--)?[a-z0-9]+(?:-[a-z0-9]+)*.){1,126}){1,}(?:(?:[a-z][a-z0-9]*)|(?:(?:xn--)[a-z0-9]+))(?:-[a-z0-9]+)*)|(?:[(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})|(?:(?!(?:.*[a-f0-9][:]]){7,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?)))|(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){5}:)|(?:(?!(?:.*[a-f0-9]:){5,})(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3})?::(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3}:)?)))?(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))(?:.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))){3}))]))$/i);

Zing! Works like a charm! Not only did I get the consistency I was looking for between front and back end validation, but I also got a more accurate regex in the process. Double win!

Thank you to all those who provided suggestions!

Wednesday, March 31, 2021
answered 7 Months ago

As you say, ? sometimes means "zero or one", but in your regex +? is a single unit meaning "one or more — and preferably as few as possible". (This is in contrast to bare +, which means "one or more — and preferably as many as possible".)

As the documentation puts it:

However, if a quantifier is followed by a question mark, then it becomes lazy, and instead matches the minimum number of times possible, so the pattern /*.*?*/ does the right thing with the C comments. The meaning of the various quantifiers is not otherwise changed, just the preferred number of matches. Do not confuse this use of question mark with its use as a quantifier in its own right. Because it has two uses, it can sometimes appear doubled, as in d??d which matches one digit by preference, but can match two if that is the only way the rest of the pattern matches.

Wednesday, March 31, 2021
answered 7 Months ago

The /u modifier is for unicode support. Support for it was added to JavaScript in ES2015.

Read to learn more information about unicode in regex with JavaScript.

Polish characters:

? u0104
? u0106
? u0118
? u0141
? u0143
Ó u00D3
? u015A
? u0179
? u017B
? u0105
? u0107
? u0119
? u0142
? u0144
ó u00F3
? u015B
? u017A
? u017C

All special Polish characters:

Wednesday, March 31, 2021
answered 7 Months ago

In JavaScript bit shifts (>>, <<) are always performed on signed, 32-bits integers. This leads to range overflow for large numbers.

Wednesday, July 14, 2021
answered 4 Months ago

You would be better off using a function as the second parameter in replace(), and you could also use a regex literal instead of the RegExp constructor:

var replaced = '-moz-border-radius'.replace(/-([a-z])/gi, function(s, group1) {
    return group1.toUpperCase();
Friday, October 8, 2021
answered 3 Weeks ago
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