select the network from metamask when first visiting

src/index.js

@@ -37,7 +37,7 @@ class AppMainRouter extends Component {
   }
 
   initChain = () => {
-    const netId = window.localStorage.netId
+    const netId = window.sessionStorage.netId
     getWeb3(netId, this.onAccountChange)
       .then(async web3Config => {
         await this.initialize(web3Config)
@@ -102,7 +102,7 @@ class AppMainRouter extends Component {
 
   onNetworkChange = e => {
     commonStore.showLoading(getNetworkBranch(e.value))
-    window.localStorage.netId = e.value
+    window.sessionStorage.netId = e.value
     contractsStore.resetContracts()
     ballotsStore.reset()
     this.initChain()

src/utils/getWeb3.js

@@ -4,9 +4,8 @@ import { constants } from './constants'
 
 const defaultNetId = helpers.netIdByBranch(constants.CORE)
 
-export default async function getWeb3(netId = defaultNetId, onAccountChange) {
+export default async function getWeb3(netId, onAccountChange) {
   let web3 = null
-  netId = Number(netId)
 
   // Checking if Web3 has been injected by the browser (Mist/MetaMask)
   if (window.ethereum) {
@@ -23,6 +22,20 @@ export default async function getWeb3(netId = defaultNetId, onAccountChange) {
     console.log('Injected web3 detected.')
   }
 
+  if (!netId) {
+    if (web3) {
+      netId = await web3.eth.net.getId()
+      if (!(netId in constants.NETWORKS)) {
+        netId = defaultNetId
+      }
+    } else {
+      netId = defaultNetId
+    }
+    window.sessionStorage.netId = netId
+  }
+
+  netId = Number(netId)
+
   const network = constants.NETWORKS[netId]
   const injectedWeb3 = web3 !== null
   let netIdName = network.NAME