Validate an email address always fails

Question

Please see the code below:

function (string regex, string value)
{
    var regularExpression = new RegExp(regex); 
    return regularExpression.test(value);
}

Why does it fail? It seems to fail for everything I enter. I got the code from here: How to validate an email address in JavaScript? i.e. the community answer that starts: "I've slightly modified Jaymon's answer".

Don't ever use `new RegExp` unless you need to create a regex dynamically, use a literal instead — CertainPerformance, Apr 22 '19 at 10:04
@CertainPerformance , how would I cast a string to a regular expression? — w0051977, Apr 22 '19 at 10:08
As you're doing in this question, but you really shouldn't - like I said, use literals instead (here you have many unnecessarily escaped characters) — CertainPerformance, Apr 22 '19 at 10:09
@CertainPerformance, please see my question now. Do you see why I need regex or is it still unnecessary? Thanks. — w0051977, Apr 22 '19 at 10:13
So you do need to create the regex dynamically - OK, see the linked canonical, you need to double-escape the backslashes — CertainPerformance, Apr 22 '19 at 10:15
Thanks, however that link does not show how to double escape the backslashes. I have tried this: regex.replace("\", "\\"); — w0051977, Apr 22 '19 at 10:27
They need to be double-escaped in the original string, before it's passed to the function. You could also use [`String.raw`](https://stackoverflow.com/questions/17863066/why-do-regex-constructors-need-to-be-double-escaped/55793086#55793086) — CertainPerformance, Apr 22 '19 at 10:43
Can I use string.raw in visual studio? I just see lots of errors with this string. Cannot believe how difficult this is. Thanks again. — w0051977, Apr 22 '19 at 10:46
I'd hope so - it's an ES2015 feature, which was ages ago, and code should probably be written in ESNext regardless, for ease of development. Your development environment should support it, but obsolete browsers may not, in which case you should (as always) use Babel to transpile the code to ES5 for production before serving to them — CertainPerformance, Apr 22 '19 at 10:49

score -1 · Accepted Answer · answered Apr 22 '19 at 10:03

-1

Try this

function validateEmail(email) {
    var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    return re.test(String(email).toLowerCase());
}

answered Apr 22 '19 at 10:03

Muhammad Hanzala

105
5

Thanks. However re is a string. – w0051977 Apr 22 '19 at 10:06
How I convert a string to a regular expression? – w0051977 Apr 22 '19 at 10:07
use new RegExp(re) – Muhammad Hanzala Apr 22 '19 at 10:21
if it is helpful, upvote or accept the answer, Thankyou! – Muhammad Hanzala Apr 22 '19 at 10:21
I will once I get this working. Were did you find this regex expression? – w0051977 Apr 22 '19 at 10:22
This does not work if I simply pass the string to the regex constructor. – w0051977 Apr 22 '19 at 10:24
`function validateEmail(email) { var re = new RegExp(/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/); return re.test(String(email).toLowerCase()); }` – Muhammad Hanzala Apr 22 '19 at 10:32
Please see my original question. The regex starts as a string. It must be casted from a string to a regex. Thanks. – w0051977 Apr 22 '19 at 10:33

Validate an email address always fails

1 Answers1