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Lets say I have a JS function which is simply throwing an error:

function() { throw "Danger, Will Robinson!"; }

This function passed in as an argument to a node.js addon and is used to construct a Nan::Callback (which should take care of making this handle persistent):

// get handle to JS function and its Tcl name Handle<Function> fun = Handle<Function>::Cast( info[0] ); Nan::Callback *pf = new Nan::Callback(fun);

I'm having problems intercepting this JS exception from C++ when the Nan::Callback is called with Call() from C++:

Nan::TryCatch tc; Local<Value> retv = pf->Call( Nan::GetCurrentContext()->Global(), objc-1, &args ); if ( tc.HasCaught() ) { printf("EXCEPTION:\n"); ...

In fact the script simply exits at the JS error and I never get back to inspect tc and the calls return value (retv) for any pending exceptions. What am I doing wrong?

ZachB
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ekarak
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1 Answers1

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Found it, this is most probably a known Nan bug. Quoting hankbao's comment on 27 Jul:

I've just encountered a related issue. We're currently using electron to pack our web app. There's a native node addon providing some functionality for the electron app. Our web app will call the addon and pass a js callback to it. The native addon store the callback in a NanCallback. It setups a TryCatch before calling the callback. However the TryCatch always fails to catch the exception thrown by the js callback. It turns out that if I call the callback with Function::Call instead of with NanCallback::Call(), exceptions can be caught

Based on this hint, I got the issue solved: I replaced the function handle from Nan::Callback with v8::Persistent<Function>, and finally got TryCatch to work as expected. The only catch: not using Nan means the code's prone to break as v8 is not exactly a stable API over time :)

ekarak
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  • Hi! Maybe changing to v8 style can solve this problem?https://stackoverflow.com/questions/45589254/invoking-some-callback-function-twice-leads-to-segmentation-fault-nan – Jasurbek Nabijonov Aug 09 '17 at 13:52