Regex Pattern working in regex tester but not in actual code [duplicate]

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 = "[email protected]";

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 = "[email protected]";

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
– Amrinder, Commented Nov 7, 2016 at 0:49

Raman Sahasi · Accepted Answer · 2016-11-04 03:43:21Z

3

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 = "[email protected]";

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.

answered Nov 4, 2016 at 3:43

Raman Sahasi

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1 Comment

Amrinder Over a year ago

But if we have to do it with a quote ?as in actual code this regex is coming from a json object.

Niyoko · Accepted Answer · 2016-11-04 03:30:03Z

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 = "[email protected]";

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

answered Nov 4, 2016 at 3:30

Niyoko

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3 Comments

Niyoko Over a year ago

@torazaburo He need explanation why it is not working with RegExp.

nomadictype Over a year ago

@torazaburo from the question: "But i want it to work with (new RegExp(pattern))"

Niyoko Over a year ago

@torazaburo OP Said: why this is happening here. Clearly he wanted an explanation

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