Regular expression produces different results depending whether it's stored in a variable or not

[romfrolov]

Version

v16.13.2

Platform

Darwin Romans-MBP.zyxel.box 22.3.0 Darwin Kernel Version 22.3.0: Thu Jan 5 20:49:43 PST 2023; root:xnu-8792.81.2~2/RELEASE_ARM64_T8103 arm64

Subsystem

No response

What steps will reproduce the bug?

1. Launch Node.js CLI

node

2. Test the following 2 paths with the same regular expression

> /\/teams(?:\/)?/g.test('/teams')
true
> /\/teams(?:\/)?/g.test('/teams/')
true

3. Declare a variable

> const re = /\/teams(?:\/)?/g;
undefined

4. Repeat the test

> re.test('/teams')
true
> re.test('/teams/')
false

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior?

Same result regardless whether the regular expression is stored in a variable or not.

What do you see instead?

Different results.

Additional information

I was also able to reproduce it in Brave console (Version 1.48.158 Chromium: 110.0.5481.77 (Official Build) (arm64)).

[cjihrig]

I've converted this to a discussion because it's not a bug. The g flag on the regular expression maintains state. When you use a regular expression literal, you are creating a new regular expression each time. When you assign it to a variable, you are reusing the same regular expression object, so the state of the g flag becomes relevant.

You can read more here: https://javascript.plainenglish.io/most-surprising-behavior-of-javascript-regular-expression-you-have-ever-seen-1ddb84539163