src/runtime_stack_trace.js

function demangle(func) {
#if DEMANGLE_SUPPORT
  var __cxa_demangle_func = Module['___cxa_demangle'] || Module['__cxa_demangle'];
  assert(__cxa_demangle_func);
  try {
    var s = func;
    if (s.startsWith('__Z'))
      s = s.substr(1);
    var len = lengthBytesUTF8(s)+1;
    var buf = _malloc(len);
    stringToUTF8(s, buf, len);
    var status = _malloc(4);
    var ret = __cxa_demangle_func(buf, 0, 0, status);
    if ({{{ makeGetValue('status', '0', 'i32') }}} === 0 && ret) {
      return UTF8ToString(ret);
    }
    // otherwise, libcxxabi failed
  } catch(e) {
    // ignore problems here
  } finally {
    if (buf) _free(buf);
    if (status) _free(status);
    if (ret) _free(ret);
  }
  // failure when using libcxxabi, don't demangle
  return func;
#else // DEMANGLE_SUPPORT
#if ASSERTIONS
  warnOnce('warning: build with  -s DEMANGLE_SUPPORT=1  to link in libcxxabi demangling');
#endif // ASSERTIONS
  return func;
#endif // DEMANGLE_SUPPORT
}

function demangleAll(text) {
  var regex =
#if WASM_BACKEND
    /_Z[\w\d_]+/g;
#else
    /__Z[\w\d_]+/g;
#endif
  return text.replace(regex,
    function(x) {
      var y = demangle(x);
      return x === y ? x : (y + ' [' + x + ']');
    });
}

function jsStackTrace() {
  var err = new Error();
  if (!err.stack) {
    // IE10+ special cases: It does have callstack info, but it is only populated if an Error object is thrown,
    // so try that as a special-case.
    try {
      throw new Error(0);
    } catch(e) {
      err = e;
    }
    if (!err.stack) {
      return '(no stack trace available)';
    }
  }
  return err.stack.toString();
}

function stackTrace() {
  var js = jsStackTrace();
  if (Module['extraStackTrace']) js += '\n' + Module['extraStackTrace']();
  return demangleAll(js);
}