Part 3: Building a Web App

In this final part of the onboarding series, you’ll build a React web application that provides a user-friendly interface for interacting with your smart contract. You’ll learn modern Web3 frontend patterns and Neutron-specific integrations.

What You’ll Build

A modern React app with:

Wallet connection (Keplr integration)
Real-time contract state display
Transaction execution with user feedback
Price monitoring from Oracle module
Responsive, beautiful UI

Prerequisites

Completed Part 2: Modules & Contracts
Node.js and npm installed
Basic React knowledge
Deployed contract from previous tutorials

Project Setup

1. Initialize React App

# Create React app with TypeScript
npx create-react-app neutron-counter-app --template typescript
cd neutron-counter-app

# Install Neutron and Cosmos dependencies
npm install @cosmjs/stargate @cosmjs/proto-signing @keplr-wallet/types
npm install @neutron-org/neutronjs @chakra-ui/react @emotion/react @emotion/styled framer-motion

# Install development dependencies
npm install --save-dev @types/node

2. Configure Environment

Create .env file:

REACT_APP_CHAIN_ID=neutron-testing-1
REACT_APP_RPC_URL=http://localhost:26657
REACT_APP_CONTRACT_ADDRESS=your_contract_address_here

3. Set Up Wallet Integration

Create src/hooks/useWallet.ts:

import { useState, useEffect } from 'react';
import { Window as KeplrWindow } from '@keplr-wallet/types';

declare global {
  interface Window extends KeplrWindow {}
}

export interface WalletState {
  address: string | null;
  isConnected: boolean;
  isConnecting: boolean;
}

export const useWallet = () => {
  const [wallet, setWallet] = useState<WalletState>({
    address: null,
    isConnected: false,
    isConnecting: false,
  });

  const connectWallet = async () => {
    if (!window.keplr) {
      alert('Please install Keplr extension');
      return;
    }

    setWallet(prev => ({ ...prev, isConnecting: true }));

    try {
      // Enable Neutron chain
      await window.keplr.enable(process.env.REACT_APP_CHAIN_ID!);
      
      // Get the offline signer
      const offlineSigner = window.keplr.getOfflineSigner(process.env.REACT_APP_CHAIN_ID!);
      const accounts = await offlineSigner.getAccounts();
      
      setWallet({
        address: accounts[0].address,
        isConnected: true,
        isConnecting: false,
      });
    } catch (error) {
      console.error('Failed to connect wallet:', error);
      setWallet(prev => ({ ...prev, isConnecting: false }));
    }
  };

  const disconnectWallet = () => {
    setWallet({
      address: null,
      isConnected: false,
      isConnecting: false,
    });
  };

  // Check if wallet is already connected on page load
  useEffect(() => {
    const checkConnection = async () => {
      if (window.keplr) {
        try {
          const key = await window.keplr.getKey(process.env.REACT_APP_CHAIN_ID!);
          setWallet({
            address: key.bech32Address,
            isConnected: true,
            isConnecting: false,
          });
        } catch (error) {
          // Not connected, do nothing
        }
      }
    };
    
    checkConnection();
  }, []);

  return {
    ...wallet,
    connectWallet,
    disconnectWallet,
  };
};

4. Create Contract Interface

Create src/hooks/useContract.ts:

import { useState, useEffect, useCallback } from 'react';
import { SigningStargateClient } from '@cosmjs/stargate';
import { MsgExecuteContract } from 'cosmjs-types/cosmwasm/wasm/v1/tx';
import { Window as KeplrWindow } from '@keplr-wallet/types';

declare global {
  interface Window extends KeplrWindow {}
}

interface ContractState {
  count: string;
  lastPrice: string;
  threshold: string;
}

interface UseContractReturn {
  contractState: ContractState | null;
  isLoading: boolean;
  increment: (amount: string) => Promise<void>;
  checkPriceAndIncrement: (amount: string) => Promise<void>;
  refreshState: () => Promise<void>;
}

export const useContract = (address: string | null): UseContractReturn => {
  const [contractState, setContractState] = useState<ContractState | null>(null);
  const [isLoading, setIsLoading] = useState(false);

  const queryContract = useCallback(async () => {
    if (!address) return;

    try {
      const client = await SigningStargateClient.connectWithSigner(
        process.env.REACT_APP_RPC_URL!,
        window.keplr!.getOfflineSigner(process.env.REACT_APP_CHAIN_ID!)
      );

      // Query contract state
      const countQuery = await client.queryContractSmart(
        process.env.REACT_APP_CONTRACT_ADDRESS!,
        { get_count: {} }
      );

      const priceQuery = await client.queryContractSmart(
        process.env.REACT_APP_CONTRACT_ADDRESS!,
        { get_last_price: {} }
      );

      const configQuery = await client.queryContractSmart(
        process.env.REACT_APP_CONTRACT_ADDRESS!,
        { get_config: {} }
      );

      setContractState({
        count: countQuery.count,
        lastPrice: priceQuery.price,
        threshold: configQuery.price_threshold,
      });
    } catch (error) {
      console.error('Failed to query contract:', error);
    }
  }, [address]);

  const executeContract = useCallback(async (msg: any) => {
    if (!address || !window.keplr) return;

    setIsLoading(true);
    try {
      const client = await SigningStargateClient.connectWithSigner(
        process.env.REACT_APP_RPC_URL!,
        window.keplr.getOfflineSigner(process.env.REACT_APP_CHAIN_ID!)
      );

      const executeMsg = {
        typeUrl: '/cosmwasm.wasm.v1.MsgExecuteContract',
        value: MsgExecuteContract.fromPartial({
          sender: address,
          contract: process.env.REACT_APP_CONTRACT_ADDRESS!,
          msg: new TextEncoder().encode(JSON.stringify(msg)),
          funds: [],
        }),
      };

      const fee = {
        amount: [{ denom: 'untrn', amount: '2000' }],
        gas: '200000',
      };

      const result = await client.signAndBroadcast(address, [executeMsg], fee);
      
      if (result.code === 0) {
        console.log('Transaction successful:', result.transactionHash);
        await queryContract(); // Refresh state
      } else {
        throw new Error(`Transaction failed: ${result.rawLog}`);
      }
    } catch (error) {
      console.error('Transaction failed:', error);
      throw error;
    } finally {
      setIsLoading(false);
    }
  }, [address, queryContract]);

  const increment = useCallback(async (amount: string) => {
    await executeContract({ increment: { amount } });
  }, [executeContract]);

  const checkPriceAndIncrement = useCallback(async (amount: string) => {
    await executeContract({ check_price_and_increment: { amount } });
  }, [executeContract]);

  const refreshState = useCallback(async () => {
    await queryContract();
  }, [queryContract]);

  // Query contract state when address changes
  useEffect(() => {
    if (address) {
      queryContract();
    }
  }, [address, queryContract]);

  return {
    contractState,
    isLoading,
    increment,
    checkPriceAndIncrement,
    refreshState,
  };
};

5. Build the UI Components

Create src/components/WalletConnect.tsx:

import React from 'react';
import { Button, Box, Text } from '@chakra-ui/react';
import { useWallet } from '../hooks/useWallet';

export const WalletConnect: React.FC = () => {
  const { address, isConnected, isConnecting, connectWallet, disconnectWallet } = useWallet();

  return (
    <Box p={4} borderWidth={1} borderRadius="md" mb={4}>
      <Text fontSize="lg" mb={2}>Wallet Connection</Text>
      {isConnected ? (
        <Box>
          <Text fontSize="sm" color="gray.600" mb={2}>
            Connected: {address?.slice(0, 10)}...{address?.slice(-8)}
          </Text>
          <Button colorScheme="red" size="sm" onClick={disconnectWallet}>
            Disconnect
          </Button>
        </Box>
      ) : (
        <Button 
          colorScheme="blue" 
          onClick={connectWallet}
          isLoading={isConnecting}
          loadingText="Connecting..."
        >
          Connect Keplr Wallet
        </Button>
      )}
    </Box>
  );
};

Create src/components/ContractInterface.tsx:

import React, { useState } from 'react';
import {
  Box,
  Text,
  Button,
  Input,
  VStack,
  HStack,
  useToast,
  Badge,
  Divider,
} from '@chakra-ui/react';
import { useWallet } from '../hooks/useWallet';
import { useContract } from '../hooks/useContract';

export const ContractInterface: React.FC = () => {
  const { address, isConnected } = useWallet();
  const { contractState, isLoading, increment, checkPriceAndIncrement, refreshState } = useContract(address);
  const [incrementAmount, setIncrementAmount] = useState('1');
  const toast = useToast();

  const handleIncrement = async () => {
    try {
      await increment(incrementAmount);
      toast({
        title: 'Success!',
        description: `Incremented counter by ${incrementAmount}`,
        status: 'success',
        duration: 5000,
        isClosable: true,
      });
    } catch (error) {
      toast({
        title: 'Error',
        description: 'Failed to increment counter',
        status: 'error',
        duration: 5000,
        isClosable: true,
      });
    }
  };

  const handlePriceIncrement = async () => {
    try {
      await checkPriceAndIncrement(incrementAmount);
      toast({
        title: 'Success!',
        description: 'Price check passed, counter incremented',
        status: 'success',
        duration: 5000,
        isClosable: true,
      });
    } catch (error) {
      toast({
        title: 'Error',
        description: 'Price check failed or increment failed',
        status: 'error',
        duration: 5000,
        isClosable: true,
      });
    }
  };

  if (!isConnected) {
    return (
      <Box p={4} borderWidth={1} borderRadius="md" textAlign="center">
        <Text>Please connect your wallet to interact with the contract</Text>
      </Box>
    );
  }

  return (
    <Box p={6} borderWidth={1} borderRadius="lg" shadow="md">
      <Text fontSize="xl" mb={4} fontWeight="bold">Smart Contract Interface</Text>
      
      {contractState && (
        <VStack align="stretch" spacing={4}>
          {/* Contract State Display */}
          <Box p={4} bg="gray.50" borderRadius="md">
            <Text fontSize="lg" mb={2}>Contract State</Text>
            <HStack justify="space-between">
              <Text>Current Count:</Text>
              <Badge colorScheme="blue" fontSize="md">{contractState.count}</Badge>
            </HStack>
            <HStack justify="space-between" mt={2}>
              <Text>Last ATOM Price:</Text>
              <Badge colorScheme="green" fontSize="md">${contractState.lastPrice}</Badge>
            </HStack>
            <HStack justify="space-between" mt={2}>
              <Text>Price Threshold:</Text>
              <Badge colorScheme="orange" fontSize="md">${contractState.threshold}</Badge>
            </HStack>
          </Box>

          <Divider />

          {/* Controls */}
          <VStack spacing={3}>
            <HStack width="100%">
              <Text>Amount to increment:</Text>
              <Input
                value={incrementAmount}
                onChange={(e) => setIncrementAmount(e.target.value)}
                placeholder="Enter amount"
                size="sm"
                width="100px"
                type="number"
                min="1"
                max="100"
              />
            </HStack>

            <VStack width="100%" spacing={2}>
              <Button
                colorScheme="blue"
                onClick={handleIncrement}
                isLoading={isLoading}
                loadingText="Processing..."
                width="100%"
              >
                Simple Increment
              </Button>
              
              <Button
                colorScheme="green"
                onClick={handlePriceIncrement}
                isLoading={isLoading}
                loadingText="Checking Price..."
                width="100%"
              >
                Price-Checked Increment
              </Button>
              
              <Button
                variant="outline"
                onClick={refreshState}
                width="100%"
                size="sm"
              >
                Refresh State
              </Button>
            </VStack>
          </VStack>
        </VStack>
      )}
    </Box>
  );
};

6. Main App Component

Update src/App.tsx:

import React from 'react';
import { ChakraProvider, Container, VStack, Heading, Text } from '@chakra-ui/react';
import { WalletConnect } from './components/WalletConnect';
import { ContractInterface } from './components/ContractInterface';

function App() {
  return (
    <ChakraProvider>
      <Container maxW="md" py={8}>
        <VStack spacing={6}>
          <VStack textAlign="center">
            <Heading size="lg">Neutron Counter DApp</Heading>
            <Text color="gray.600">
              A decentralized counter with Oracle price integration
            </Text>
          </VStack>
          
          <WalletConnect />
          <ContractInterface />
          
          <Text fontSize="sm" color="gray.500" textAlign="center">
            Built with React, CosmJS, and Neutron
          </Text>
        </VStack>
      </Container>
    </ChakraProvider>
  );
}

export default App;

Advanced Features

1. Transaction History

Add transaction monitoring:

// In useContract hook
const [transactions, setTransactions] = useState<Array<{
  hash: string;
  type: string;
  timestamp: number;
  status: 'pending' | 'success' | 'failed';
}>>([]);

const executeContract = useCallback(async (msg: any, type: string) => {
  // ... existing code ...
  
  const txId = Date.now().toString();
  setTransactions(prev => [...prev, {
    hash: txId,
    type,
    timestamp: Date.now(),
    status: 'pending'
  }]);

  try {
    const result = await client.signAndBroadcast(address, [executeMsg], fee);
    
    setTransactions(prev => 
      prev.map(tx => 
        tx.hash === txId 
          ? { ...tx, hash: result.transactionHash, status: 'success' }
          : tx
      )
    );
  } catch (error) {
    setTransactions(prev => 
      prev.map(tx => 
        tx.hash === txId 
          ? { ...tx, status: 'failed' }
          : tx
      )
    );
    throw error;
  }
}, [address, queryContract]);

2. Real-time Updates

Add WebSocket connection for real-time updates:

useEffect(() => {
  const ws = new WebSocket('ws://localhost:26657/websocket');
  
  ws.onmessage = (event) => {
    const data = JSON.parse(event.data);
    if (data.result?.events?.some((e: any) => 
      e.type === 'wasm' && 
      e.attributes?.some((a: any) => 
        a.key === 'contract_address' && 
        a.value === process.env.REACT_APP_CONTRACT_ADDRESS
      )
    )) {
      queryContract(); // Refresh on contract events
    }
  };
  
  return () => ws.close();
}, [queryContract]);

3. Error Boundaries

Create src/components/ErrorBoundary.tsx:

import React, { Component, ReactNode } from 'react';
import { Box, Text, Button } from '@chakra-ui/react';

interface Props {
  children: ReactNode;
}

interface State {
  hasError: boolean;
  error?: Error;
}

export class ErrorBoundary extends Component<Props, State> {
  constructor(props: Props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(error: Error): State {
    return { hasError: true, error };
  }

  render() {
    if (this.state.hasError) {
      return (
        <Box p={6} textAlign="center">
          <Text fontSize="xl" mb={4}>Something went wrong</Text>
          <Text fontSize="sm" color="gray.600" mb={4}>
            {this.state.error?.message}
          </Text>
          <Button onClick={() => this.setState({ hasError: false })}>
            Try Again
          </Button>
        </Box>
      );
    }

    return this.props.children;
  }
}

Deployment

1. Build for Production

# Build the app
npm run build

# Serve locally to test
npx serve -s build

2. Deploy to IPFS

# Install IPFS CLI
npm install -g ipfs-http-client

# Add build folder to IPFS
ipfs add -r build/

# Pin the hash for persistence
ipfs pin add YOUR_HASH_HERE

3. Configure for Mainnet

Update .env for mainnet:

REACT_APP_CHAIN_ID=neutron-1
REACT_APP_RPC_URL=https://rpc-neutron.cosmos.directory
REACT_APP_CONTRACT_ADDRESS=your_mainnet_contract_address

Key Features Implemented

Wallet Integration: Seamless Keplr wallet connection
Contract Interaction: Execute and query smart contract functions
Real-time Updates: Live contract state monitoring
Error Handling: Comprehensive error boundaries and user feedback
Responsive Design: Modern, mobile-friendly interface
Oracle Integration: Display live price data from Neutron’s Oracle module

Security Best Practices

Input Validation: Always validate user inputs
Error Handling: Never expose sensitive error details
State Management: Keep sensitive data out of global state
Environment Variables: Use environment variables for configuration
HTTPS: Always serve over HTTPS in production

Next Steps

Congratulations! You’ve built a complete DApp on Neutron. Consider exploring:

Advanced UI: Add charts, animations, and better UX
Multi-contract Integration: Interact with multiple contracts
Cross-chain Features: Use ICQ to display data from other chains
Testing: Add comprehensive unit and integration tests
Mobile App: Build a React Native version

Troubleshooting

Keplr Not Detected

Ensure Keplr extension is installed and enabled. Handle the case where Keplr is not available.

Transaction Fails

Check gas limits, fee amounts, and contract message format. Use browser dev tools to debug.

State Not Updating

Ensure you’re calling refreshState() after successful transactions and handling async operations properly.

You’ve now completed the full Neutron development journey from smart contract to web app! 🎉

Getting Started

Tutorials

Modules

What You’ll Build

Prerequisites

Project Setup

1. Initialize React App

2. Configure Environment

3. Set Up Wallet Integration

4. Create Contract Interface

5. Build the UI Components

6. Main App Component

Advanced Features

1. Transaction History

2. Real-time Updates

3. Error Boundaries

Deployment

1. Build for Production

2. Deploy to IPFS

3. Configure for Mainnet

Key Features Implemented

Security Best Practices

Next Steps

Troubleshooting

Getting Started

Tutorials

Modules

​What You’ll Build

​Prerequisites

​Project Setup

​1. Initialize React App

​2. Configure Environment

​3. Set Up Wallet Integration

​4. Create Contract Interface

​5. Build the UI Components

​6. Main App Component

​Advanced Features

​1. Transaction History

​2. Real-time Updates

​3. Error Boundaries

​Deployment

​1. Build for Production

​2. Deploy to IPFS

​3. Configure for Mainnet

​Key Features Implemented

​Security Best Practices

​Next Steps

​Troubleshooting

What You’ll Build

Prerequisites

Project Setup

1. Initialize React App

2. Configure Environment

3. Set Up Wallet Integration

4. Create Contract Interface

5. Build the UI Components

6. Main App Component

Advanced Features

1. Transaction History

2. Real-time Updates

3. Error Boundaries

Deployment

1. Build for Production

2. Deploy to IPFS

3. Configure for Mainnet

Key Features Implemented

Security Best Practices

Next Steps

Troubleshooting