code: function (filename, lineNum, callsiteFrameIdx, stackFrames) {
      this.filename         = filename;
      this.lineNum          = lineNum;
      this.callsiteFrameIdx = callsiteFrameIdx;
      this.stackFrames      = stackFrames;
      this.isV8Frames       = isV8StackFrame(this.stackFrames[0]);
  }
docs: CallsiteRecord