code: func (sw *stackWrapper) peek(idx int) *big.Int {
  	if len(sw.stack.Data()) <= idx {
  		// TODO(karalabe): We can't js-throw from Go inside duktape inside Go. The Go
  		// runtime goes belly up https://github.com/golang/go/issues/15639.
  		log.Warn("Tracer accessed out of bound stack", "size", len(sw.stack.Data()), "index", idx)
  		return new(big.Int)
  	}
  	return sw.stack.Data()[len(sw.stack.Data())-idx-1]
  }
docs: // peek returns the nth-from-the-top element of the stack.