Regex Pattern working in regex tester but not in actual code

Question

The following regex check is not working in the code. But if i use this pattern at regex101.com it works perfectly

var pattern = "^([a-zA-Z0-9]([-\.\w]*[a-zA-Z0-9])*@([a-zA-Z0-9][-\w]*[a-zA-Z0-9]\.)+[a-zA-Z]{2,9})$";
var value = "test@user.com";

var regexp = new RegExp(pattern);
if (!regexp.test(value)) {
   alert("Failed");
} else {
 alert("passed");
}

Could you please help me why this is happening here. By the way if i make some modifications like given below, it works. But i want it to work with (new RegExp(pattern))

var pattern = /^([a-zA-Z0-9]([-\.\w]*[a-zA-Z0-9])*@([a-zA-Z0-9][-\w]*[a-zA-Z0-9]\.)+[a-zA-Z]{2,9})$/;
var value = "test@user.com";

if (!pattern.test(value)) {
   alert("Failed");
} else {
 alert("passed");
}

@torazaburo got the answer.. I need to add extra backslash in regular expression infront of each backslash. because "new regExp(pattern)" was stripping backslashes from the pattern and thats why it was not working. — Amrinder, Nov 07 '16 at 00:49

score 3 · Answer 1 · answered Nov 04 '16 at 03:43

Just remove the double quotes and put your Regex simply in forward slashes.

var pattern = /^([a-zA-Z0-9]([-\.\w]*[a-zA-Z0-9])*@([a-zA-Z0-9][-\w]*[a-zA-Z0-9]\.)+[a-zA-Z]{2,9})$/;
var value = "test@user.com";

var regexp = new RegExp(pattern);
if (!regexp.test(value)) {
   alert("Failed");
} else {
 alert("passed");
}

It's because, if you're putting double quotes, then you need to escape your regular expression

However, you can simply put your regular expression as it is when placing it between forward slashes.

But if we have to do it with a quote ?as in actual code this regex is coming from a json object. — Amrinder, Nov 04 '16 at 03:51

score 0 · Answer 2 · answered Nov 04 '16 at 03:30

0

You need to escape those backslashes (\).

var pattern = "^([a-zA-Z0-9]([-\\.\\w]*[a-zA-Z0-9])*@([a-zA-Z0-9][-\\w]*[a-zA-Z0-9]\\.)+[a-zA-Z]{2,9})$";
var value = "test@user.com";

var regexp = new RegExp(pattern);
if (!regexp.test(value)) {
   console.log("Failed");
} else {
 console.log("passed");
}

answered Nov 04 '16 at 03:30

Niyoko

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@torazaburo He need **explanation** why it is not working with `RegExp`. – Niyoko Nov 04 '16 at 03:32
@torazaburo from the question: "But i want it to work with (new RegExp(pattern))" – nomadictype Nov 04 '16 at 03:32
@torazaburo OP Said: *why this is happening here*. Clearly he wanted an **explanation** – Niyoko Nov 04 '16 at 03:33

Regex Pattern working in regex tester but not in actual code

2 Answers2