Another Emscripten failure with custom output stream

ERRORS

$ make clean run > RESULT ^ ERRORS

$ head -50 ERRORS

/Users/skale/Projekty/cannot-read-fd/why-not-works.js:8182
$67,$90,$93,$102,$147) } catch(e) { if (typeof e != "number") throw e; if (ABO
                                                                    ^
TypeError: Property '10696' of object 0,0,function __ZNSt3__18messagesIwED0Ev($this){
 var label=0;


 var $1=(($this)|0);
 __ZNSt3__114__shared_countD2Ev($1);
 var $2=$this;
 __ZdlPv($2);
 return;
},0,function __ZNSt3__17num_getIcNS_19istreambuf_iteratorIcNS_11char_traitsIcEEEEED0Ev($this){
 var label=0;


 var $1=(($this)|0);
 __ZNSt3__114__shared_countD2Ev($1);
 var $2=$this;
 __ZdlPv($2);
 return;
},0,function __ZNKSt3__18numpunctIcE12do_falsenameEv($agg_result,$this){
 var label=0;


 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcj($agg_result,1232,5);
 return;
},0,function __ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_($__os){
 var label=0;
 var sp=STACKTOP;STACKTOP=(STACKTOP+8)|0; (assert((STACKTOP|0) < (STACK_MAX|0))|0);
 label = 1;
 while(1)switch(label){
 case 1:
 var $1;
 var $2;
 var $3;
 var $4;
 var $5;
 var $6=sp;
 var $7;
 var $8;
 var $9;
 $9=$__os;
 var $10=$9;
 var $11=$9;
 var $12=$11;
 var $13=HEAP32[(($12)>>2)];
 var $14=((($13)-(12))|0);
 var $15=$14;
 
 $ tail -50 ERRORS
 
  case 3:
 __ZdaPv($10);
 label=4;break;
 case 4:
 var $13=(($this)|0);

 var $14=$this;
 __ZdlPv($14);
 return;
  default: assert(0, "bad label: " + label);
 }

},0,function __ZNSt3__113basic_istreamIwNS_11char_traitsIwEEED0Ev($this){
 var label=0;


 var $1=(($this+8)|0);
 __ZNSt3__18ios_baseD2Ev($1);
 var $2=$this;
 __ZdlPv($2);
 return;
},0,function ___cxx_global_array_dtor120($0){
 var label=0;


 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12220);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12208);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12196);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12184);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12172);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12160);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12148);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12136);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12124);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12112);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12100);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12088);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12076);
 __ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEED1Ev(12064);
 return;
},0 is not a function
    at __ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_ (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:12162:31)
    at /Users/skale/Projekty/cannot-read-fd/why-not-works.js:8182:44
    at __ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:8182:290)
    at _print_it (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:7965:9)
    at ccallFunc (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:612:24)
    at Object.ccall (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:569:10)
    at null._onTimeout (/Users/skale/Projekty/cannot-read-fd/why-not-works.js:2339:16)
    at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
make: *** [run] Error 8

helper.js

mergeInto(LibraryManager.library, {
  try_from_js: function() {
    Module.ccall('print_it', 'number', ['string'], ["From `try_from_js` it works."]);
    setTimeout(function() {
      // It could be also nodejs' readline's `on('line', …)` callback.
      Module.ccall('print_it', 'number', ['string'], ["From `setTimeout` callback it fails."]);
    }, 0);
  }
});

Makefile

TARGET = why-not-works.js

OBJS = src.bc
HLPS = helper.js

CXX = emcc

LDFLAGS = \
  -s EXPORTED_FUNCTIONS="['_print_it', '_main']" \
  --js-library helper.js

.PHONY: run clean default

$(TARGET): $(OBJS) $(HLPS)
	$(CXX) -o $@ $(OBJS) $(LDFLAGS)

%.bc: %.cpp
	$(CXX) $< -o $@

default: $(TARGET)

clean:
	- rm $(TARGET) *.bc

run: $(TARGET)
	node $(TARGET)

RESULT

$ make clean run > RESULT ^ ERRORS
$ cat RESULT
rm why-not-works.js *.bc
emcc src.cpp -o src.bc
emcc -o why-not-works.js src.bc -s EXPORTED_FUNCTIONS="['_print_it', '_main']" --js-library helper.js
node why-not-works.js
 * From `main` it works.

 * From `try_from_js` it works.

src.cpp

#import <emscripten.h>
#import <iostream>
#import <sstream>

class EventedOStream : public std::ostream {

private:
  class EventedBuf : public std::stringbuf {
  public:
   ~EventedBuf() { pubsync(); }
    int sync();
  };

public:
  EventedOStream() : std::ostream(new EventedBuf) {}
 ~EventedOStream() { delete rdbuf(); }

};

EventedOStream eout;

extern "C" void try_from_js();

extern "C" int print_it(const char* str) {
  eout << " * " << str << std::endl;
  return 0;
}

int main(int argc, char* argv[]) {
  print_it("From `main` it works.");
  try_from_js();
  return 0;
}

int EventedOStream::EventedBuf::sync() {
  if(!str().empty()) {
    EM_ASM_INT({
      console.log(Pointer_stringify($0));
    }, str().c_str());
  }
  str("");
  return 0;
}