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Deploying and Interacting with Your Contract

Let's deploy your randomness contract and interact with it on NEAR testnet.

Prerequisites​

Ensure you have:

  • NEAR CLI installed: npm install -g near-cli-rs
  • A testnet account: create one at mynearwallet.com
  • Your contract compiled (.wasm file)

Creating a Dev Account​

The easiest way to deploy for testing:

# Deploy to a dev account (creates new account automatically)
near dev-deploy build/coin_flip.wasm

# Note the deployed account ID (e.g., dev-1234567890123-12345678901234)
export CONTRACT_ID=dev-1234567890123-12345678901234

Deploying to a Named Account​

For production or persistent testing:

# Create a subaccount
near account create-account sponsor-by-faucet-service coin-flip.YOUR_ACCOUNT.testnet autogenerate-new-keypair save-to-keychain network-config testnet create

# Deploy the contract
near contract deploy coin-flip.YOUR_ACCOUNT.testnet use-file ./build/coin_flip.wasm without-init-call network-config testnet sign-with-keychain send

Interacting with the Contract​

Playing the Coin Flip Game​

# Flip the coin (guess heads)
near contract call-function as-transaction $CONTRACT_ID flip_coin json-args '{"player_guess":"heads"}' prepaid-gas '30 TeraGas' attached-deposit '0 NEAR' sign-as YOUR_ACCOUNT.testnet network-config testnet sign-with-keychain send

# Check your points
near contract call-function as-read-only $CONTRACT_ID points_of json-args '{"player":"YOUR_ACCOUNT.testnet"}' network-config testnet now

Building a Simple Frontend​

Create a basic web interface:

<!DOCTYPE html>
<html>
<head>
    <title>NEAR Coin Flip</title>
    <script src="https://cdn.jsdelivr.net/npm/near-api-js/dist/near-api-js.min.js"></script>
</head>
<body>
    <h1>Coin Flip Game</h1>
    <button onclick="flip('heads')">Heads</button>
    <button onclick="flip('tails')">Tails</button>
    <div id="result"></div>
    <div id="points"></div>

    <script>
        const CONTRACT_ID = 'coinflip.near-examples.testnet';
        
        async function flip(guess) {
            const keyStore = new nearApi.keyStores.BrowserLocalStorageKeyStore();
            const config = {
                networkId: "testnet",
                keyStore,
                nodeUrl: "https://rpc.testnet.near.org",
                walletUrl: "https://testnet.mynearwallet.com",
            };
            
            const near = await nearApi.connect(config);
            const wallet = new nearApi.WalletConnection(near);
            
            if (!wallet.isSignedIn()) {
                wallet.requestSignIn({ contractId: CONTRACT_ID });
                return;
            }
            
            const account = wallet.account();
            const result = await account.functionCall({
                contractId: CONTRACT_ID,
                methodName: 'flip_coin',
                args: { player_guess: guess }
            });
            
            document.getElementById('result').innerText = 
                `Result: ${result}`;
            
            updatePoints();
        }
        
        async function updatePoints() {
            // View function call to get points
            const points = await near.connection.provider.query({
                request_type: "call_function",
                account_id: CONTRACT_ID,
                method_name: "points_of",
                args_base64: btoa(JSON.stringify({
                    player: wallet.getAccountId()
                })),
                finality: "optimistic",
            });
            
            document.getElementById('points').innerText = 
                `Points: ${JSON.parse(atob(points.result))}`;
        }
    </script>
</body>
</html>

Using the Example Frontend​

The repository includes a complete Next.js frontend:

# Navigate to frontend directory
cd frontend

# Install dependencies
npm install

# Run development server
npm run dev

# Open http://localhost:3000

The frontend demonstrates:

  • Wallet integration with multiple wallet providers
  • Real-time game interactions
  • Score tracking
  • Animated coin flips

Monitoring Your Contract​

View contract activity:

# Check recent transactions
near account view-account-summary $CONTRACT_ID network-config testnet now

# View contract state size
near contract view-state $CONTRACT_ID view-state-all network-config testnet now

Best Practices for Production​

  1. Set up monitoring for randomness distribution
  2. Implement rate limiting to prevent spam
  3. Add events for important actions
  4. Consider upgradability patterns
  5. Audit your randomness usage regularly

Next Steps​

  • Build more complex games using randomness patterns
  • Add social features like leaderboards
  • Implement different game modes
  • Study other randomness use cases in DeFi and NFTs

Congratulations! You've learned how to implement secure on-chain randomness in NEAR smart contracts.