Regular Expression from String gives null in Javascript

Question

I have a string

let str = 'WordA<br>WordB';

I am using this expression /(\S+)(?=<br>)/ to match characters before the <br>.

It works fine directly as a predefined function

let regex = /(\S+)(?=<br>)/;

But when I try to build it using a string, it gives null everytime.

let rgs = "(\S+)(?=<br>)";
let regex = new RegExp(rgs);

How to use the regex as a string to obtain the same results.

Full code:

let str = 'WordA<br>WordB';
let regex = /(\S+)(?=<br>)/;

let m = str.match(regex);
console.log(m);
console.log(m[1]);

let rgs = ("(\S+)(?=<br>)");
let regex2 = new RegExp(rgs);
let m2 = str.match(regex2);
console.log(m2);
console.log(m2[1]);

in other words - you need to escape the escape character.

Bekim Bacaj
– Bekim Bacaj

2017-10-29 09:59:48 +00:00
Commented Oct 29, 2017 at 9:59 — Bekim Bacaj
– Bekim Bacaj, Commented Oct 29, 2017 at 9:59

Martin Adámek · Accepted Answer · 2017-10-29 09:57:17Z

2

When using regex in string via new RegExp(), you need to escape the backslash character:

let str = 'WordA<br>WordB';
let regex = /(\S+)(?=<br>)/;

let m = str.match(regex);
console.log(m);
console.log(m[1]);

let rgs = "(\\S+)(?=<br>)";
let regex2 = new RegExp(rgs);
let m2 = str.match(regex2);
console.log(m2);
console.log(m2[1]);

Otherwise the "\S" is translated to just "S" (as you are escaping the S character):

console.log("S", "\S", "\\S", "S" === "\S");

edited Oct 29, 2017 at 9:57

answered Oct 29, 2017 at 9:52

Martin Adámek

18.6k5 gold badges52 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Regular Expression from String gives null in Javascript

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related