How do I obtain the pending script exception?

[AnsisMalins]

I get an exception "The V8 runtime cannot perform the requested operation because a script exception is pending". So what is the script exception? Where is it? How do I obtain it? Where in ClearScript or V8 do I set a breakpoint to see that exception being "pended"?

[ClearScriptLib]

Hi @AnsisMalins,

I get an exception "The V8 runtime cannot perform the requested operation because a script exception is pending". So what is the script exception? Where is it? How do I obtain it? Where in ClearScript or V8 do I set a breakpoint to see that exception being "pended"?

Unfortunately, we don't have a simple answer for you. Depending on the context, that exception message could be misleading.

V8's C++ API uses maybe types for nearly all returned data. If a V8 API call returns an empty result, it could be for a number of reasons, including that the call failed due to a pending script exception.

There's no way to determine the exact cause. If a script exception is thrown, ClearScript eventually catches it and converts it to a managed exception with a better error message. But if a V8 API call returns an empty result while no script is executing, it could be due to a number of less predictable conditions – out-of-memory, internal error, etc.

One situation in which we've seen this happen is as follows:

1. During script execution, a JavaScript exception is thrown.
2. V8 unwinds the script stack and performs other housekeeping before returning to ClearScript.
3. During that process, V8 decides to call ClearScript for some other reason – e.g., to retrieve a managed object's property, etc.
4. ClearScript calls the host to fulfill V8's request.
5. The host makes an attempt to re-enter the script engine.

That nested attempt to engage the script engine could result in the exception you're seeing – a script exception is pending, but ClearScript hasn't had a chance to handle it yet.

If you have a reproducible case, please let us know.

Thanks!