How to use the web3-provider-engine/subproviders/rpc function in web3-provider-engine

connect ({dispatch, commit, getters, state}) {
    let providerEngine = null
    if (window.web3) {
      providerEngine = window.web3.currentProvider
    } else {
      const ROPSTEN_ENDPOINT = 'https://infura.io'

      providerEngine = new ProviderEngine()
      providerEngine.addProvider(new FilterSubprovider())
      providerEngine.addProvider(new RpcSubprovider({rpcUrl: ROPSTEN_ENDPOINT}))
      providerEngine.start()
    }

    zeroEx = new ZeroEx(providerEngine)
    zeroEx._web3Wrapper.web3.version.getNetwork((error, response) => {
      if (error) console.error(error)
      if (parseInt(response) === 42 && window.location.hostname !== 'kovan.0xchange.me') {
        window.location.href = 'https://kovan.0xchange.me'
      } else if (parseInt(response) === 1 && window.location.hostname === 'kovan.0xchange.me') {
        window.location.href = 'https://0xchange.me'
      }
    })
    // commit('SET_ZERO_EX', zeroEx)
    // 3117574 kovan
    // 4145578 mainnet
    // zeroEx.exchange.getLogsAsync('LogFill', {fromBlock: 4219261, toBlock: 'latest'}, {}).then((logs) => {

const initWeb3 = async function () {
  // Checking if Web3 has been injected by the browser (Mist/MetaMask/Parity)
  if (typeof window.web3 !== 'undefined') {
    console.info('web3 already exists');
    externalWeb3 = true;
  } else {
    const dummyWeb3 = new Web3(new Web3.providers.HttpProvider(NODE_URL));
    const getNetworkId = promisify(dummyWeb3.version.getNetwork);

    const engine = new ProviderEngine();
    const ledgerWalletSubProvider = await LedgerWalletSubproviderFactory(getNetworkId, Config.derivationPath, true);

    ledger = ledgerWalletSubProvider.ledger;
    engine.addProvider(ledgerWalletSubProvider);
    engine.addProvider(new RpcSubprovider({
      rpcUrl: NODE_URL,
    }));
    engine.start();
    window.web3 = new Web3(engine);
    externalWeb3 = false;
  }
};

return (_network, _web3) => {
            ethNetwork = Network.fromJson(_network);

            const rpcUrl = `${ethNetwork.fullhost()}`;

            const engine = new ProviderEngine();
            const web3 = new _web3(engine);

            const walletSubprovider = new HookedWalletSubprovider(new ScatterEthereumWallet());
            engine.addProvider(walletSubprovider);

            if(ethNetwork.protocol.indexOf('http') > -1) engine.addProvider(new RpcSubprovider({rpcUrl}));
            else engine.addProvider(new WebsocketSubprovider({rpcUrl}));

            engine.start();

            return web3;
        }
    }

constructor(opts) {
    const rpcUrl = opts.rpcUrl || 'http://localhost:8545'
    const engine = new ProviderEngine()
    const subprovider = new WalletConnectSubprovider(opts)
    engine.addProvider(subprovider)
    engine.addProvider(new RpcSubprovider({ rpcUrl }))
    engine.start()
  }
}

const getCachedInstance = (network, wallet = null) => {
    const key = network.unique() + (wallet ? wallet.getAccounts()[0] : '');
    if(cachedInstances.hasOwnProperty(key)) return cachedInstances[key];
    else {
        const engine = new ProviderEngine();
        const web3 = new Web3(engine);
        if(wallet) engine.addProvider(new HookedWalletSubprovider(wallet));

        const rpcUrl = network.host === 'ethnodes.get-scatter.com' ? 'https://commonly-classic-katydid.quiknode.io/d0bf98e7-a866-43d4-ac71-2397fd1b3aba/dQsznyrZRg2dr4DQJNPDgw==/' : network.fullhost();
        engine.addProvider(new RpcSubprovider({rpcUrl}));
        engine.start();
        cachedInstances[key] = [web3, engine];
        return cachedInstances[key];
    }
}

export const getDefaultWeb3 = () => {
  const engine = new ProviderEngine()
  engine.addProvider(
    new RpcSubprovider({
      rpcUrl: RPC_HOST
    })
  )
  engine.start()
  return {
    web3: new Web3(engine)
  }
}