code: func (api *PublicEthereumAPI) ChainId() hexutil.Uint64 {
  	chainID := new(big.Int)
  	if config := api.e.blockchain.Config(); config.IsEIP155(api.e.blockchain.CurrentBlock().Number()) {
  		chainID = config.ChainID
  	}
  	return (hexutil.Uint64)(chainID.Uint64())
  }
docs: // ChainId is the EIP-155 replay-protection chain id for the current ethereum chain config.