Undefined RegExp always match

[miguelaeh]

• Version: 12.20.0

• Platform: Linux 4.15.0-132-generic Introduce the Nil Object #136-Ubuntu SMP Tue Jan 12 14:58:42 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

• Subsystem:

What steps will reproduce the bug?

Hi, I am not totally sure if this is a bug or if it is expected, but it seems to be a problematic behavior.
Execute the following NodeJS code. Creting a RegExp with an undefined variable will always match any string:

const str="hello";
const regex = undefined;
str.match(new RegExp(regex));

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

Always

What is the expected behavior?

I am not totally sure if this is unexpected, but IMHO I would expect an error when trying to create an undefined regular expression.

What do you see instead?

I see that the undefined regex matches always any string. It produces unexpected outputs if you use it, for example, to test a match inside an if.

Additional information

[cjihrig]

undefined is treated as the empty string in the RegExp constructor. The JavaScript specification dictates this behavior, and it is implemented in V8, so it is out of Node's control.