instanceof not working in preview-server

[rothsandro]

Describe the Bug

After updating to react-email v5 and installing @react-email/preview-server, the instanceof operator is not working anymore with JS built-in types like RegExp or Array.

The following email should render "true" but renders "false" in the preview. It works fine when rendering the email with @react-email/render.

const Demo = () => {
  return <div>{`${/.+/ instanceof RegExp}`}</div>;
};

export default Demo;

This breaks libraries like Zod when using z.templateLiteral(["foo", z.number()]) because they internally use the instanceof operator.

It affects the @react-email/preview-server package but that's not available in the list below.

Which package is affected (leave empty if unsure)

No response

Link to the code that reproduces this issue

https://github.com/rothsandro/repro.react-email-instanceof

To Reproduce

Render an email with the following content and run the preview server.

const Demo = () => <div>{`${/.+/ instanceof RegExp}`}</div>

Expected Behavior

instanceof should work for JS types as it did in v4

What's your node version? (if relevant)

22.19

[gabrielmfern]

Hey, should be fixed in @react-email/preview-server@5.2.0-canary.2 and react-email@5.2.0-canary.2. Can you try them out?