Unhandled exceptions handling brought back.

lib/system/jssys.nim

@@ -37,6 +37,7 @@ type
 
 var
   framePtr {.importc, nodecl, volatile.}: PCallFrame
+  excHandler {.importc, nodecl, volatile.}: int = 0
   lastJSError {.importc, nodecl, volatile.}: PJSError = nil
 
 {.push stacktrace: off, profiler:off.}
@@ -94,15 +95,38 @@ proc rawWriteStackTrace(): string =
   else:
     result = "No stack traceback available\n"
 
+proc unhandledException(e: ref Exception) {.
+    compilerproc, asmNoStackFrame.} =
+  when NimStackTrace:
+    var buf = rawWriteStackTrace()
+  else:
+    var buf = ""
+    if e.msg != nil and e.msg[0] != '\0':
+      add(buf, "Error: unhandled exception: ")
+      add(buf, e.msg)
+    else:
+      add(buf, "Error: unhandled exception")
+    add(buf, " [")
+    add(buf, e.name)
+    add(buf, "]\n")
+    alert(buf)
+
 proc raiseException(e: ref Exception, ename: cstring) {.
     compilerproc, asmNoStackFrame.} =
   e.name = ename
+  if excHandler == 0:
+    unhandledException(e)
   asm "throw `e`;"
 
 proc reraiseException() {.compilerproc, asmNoStackFrame.} =
   if lastJSError == nil:
     raise newException(ReraiseError, "no exception to reraise")
   else:
+    if excHandler == 0:
+      var isNimException : bool
+      asm "`isNimException` = lastJSError.m_type;"
+      if isNimException:
+        unhandledException(cast[ref Exception](lastJSError))
     asm "throw lastJSError;"
 
 proc raiseOverflow {.exportc: "raiseOverflow", noreturn.} =