Error log 'toLowerCase' when next pages router changed

[cleanhyune]

Issue Title

Error log 'toLowerCase' when next pages router changed

Description

There is no error when the script is first imported, but an error occurs on a certain page.
(At this point, we’re unable to identify the exact structure or condition under which it happens.)

Expected behavior:

No error log

Actual behavior:

Print error log

OS:

Mac

Version:

0.0.70

Browser/Runtime (if applicable):

Chorme / 142.0.7444.176

Project version:

next: 15.5.7
react: 19.2.1

Logs / Screenshots

index.global.js:43 Uncaught TypeError: Cannot read properties of undefined (reading 'toLowerCase')
at window.addEventListener.signal (index.global.js:43:7102)
window.addEventListener.signal @ index.global.js:43

[aidenybai]

@cleanhyune pushed a fix, are you still able to repro?

[cleanhyune]

@aidenybai Hi, The toLowerCase error has disappeared, but the new error log below has started appearing 5 to 6 times.

Uncaught TypeError: Illegal invocation
    at HTMLDocument.St (index.global.js:43:7084)

[tt-a1i]

Hi, I took a look at the codebase and found a few places that might be related to this Illegal invocation error.

The error message HTMLDocument.St suggests it's happening in a document event listener. Looking at core.tsx, there's some KeyboardEvent prototype patching around line 1426-1456:

const originalKey = originalKeyDescriptor?.get
  ? originalKeyDescriptor.get.call(event)
  : event.key;

Calling native getters via .call() can throw Illegal invocation if the event object is in a weird state - which might happen during Next.js page transitions when DOM gets cleaned up.

The fact that it appears "5-6 times" also makes sense since there are multiple event listeners (keydown, keyup, keypress) registered on document.

Not 100% sure this is the root cause, but wrapping in try-catch might help narrow it down. Another area worth checking is event.composedPath() in is-event-from-overlay.ts.

[aidenybai]

thanks for the hint @tt-a1i ! @cleanhyune just pushed up another fix. try again?

[cleanhyune]

@aidenybai Morning, Illegal invocation has disappeared and toLowerCase error log has reappeared.
What's interesting is that while the toLowerCase error didn't occur in previous versions, it has reappeared in 0.0.76.

[tt-a1i]

Interesting - looks like the try-catch fix for Illegal invocation is working (commit 98ef97f).

For the toLowerCase error coming back, there are a few unprotected calls in the codebase. One likely culprit is in context.ts:141:

const tagName = element.tagName.toLowerCase();

If the element gets destroyed during page transitions (common in Next.js router changes), element.tagName could be undefined.

A quick fix would be:

const tagName = (element.tagName || "").toLowerCase();

Same pattern might be needed in agent.ts:180 and context.ts:183.