sign.js

api.post('/', async (req, res) => {
    const serializedTx = req.body.serializedTx;
    try {
      web3.eth.sendSignedTransaction(serializedTx)
      .on('receipt', receipt => {
        return res.status(200).json({
          code: 0,
          message: 'success',
          response: {
            txhash: receipt.transactionHash,
          }
        });
      })
      .on('error', error => {
        return res.status(400).json({
          code: 1,
          message: error.message,
        });
      });
    } catch (err) {
      return res.status(400).json({
        code: 1,
        message: err.message,
      });
    }
  });

api.post('/make', async (req, res) => {
    const privateKey = new Buffer(req.body.privateKey, 'hex');
    if (!ethUtil.isValidPrivate(privateKey)) {
      return res.status(400).json({
        code: 1,
        message: `private key length is invalid`,
      });
    }
    const rawTx = req.body.rawTx;
    const tx = new Tx(rawTx);
    tx.sign(privateKey);

    const serializedTx = tx.serialize();

    return res.status(200).json({
      code: 0,
      message: 'success',
      response: {
        serializedTx: '0x' + serializedTx.toString('hex'),
      }
    })
  });