Midnight TypeScript SDK Quick Reference

Guide for integrating Midnight contracts with TypeScript applications.

When to Use

Reference this guide when:

• Building a frontend for a Midnight dApp
• Connecting the Lace wallet
• Deploying or calling contracts from TypeScript
• Handling errors from the SDK
• Building transaction flows

---

Installation

npm install @midnight-ntwrk/midnight-js-contracts

---

Core Types

Contract Deployment

import { deployContract, ContractDeployment } from '@midnight-ntwrk/midnight-js-contracts';

const deployment: ContractDeployment = await deployContract({
  contract: compiledContract,
  privateState: initialPrivateState,
  args: constructorArgs,
});

const { contractAddress, initialState } = deployment;

Contract Interaction

import { callContract } from '@midnight-ntwrk/midnight-js-contracts';

// Call a circuit
const result = await callContract({
  contractAddress,
  circuitName: 'increment',
  args: [amount],
  privateState: currentPrivateState,
});

// Result contains new state and return value
const { newPrivateState, returnValue, proof } = result;

Providers

import {
  MidnightProvider,
  createMidnightProvider
} from '@midnight-ntwrk/midnight-js-contracts';

const provider = await createMidnightProvider({
  indexer: 'https://indexer.testnet.midnight.network',
  node: 'https://node.testnet.midnight.network',
  proofServer: 'https://prover.testnet.midnight.network',
});

---

State Management

interface ContractState<T> {
  publicState: PublicState;
  privateState: T;
}

// Subscribe to state changes
provider.subscribeToContract(contractAddress, (state) => {
  console.log('New state:', state);
});

---

Transaction Building

import { buildTransaction } from '@midnight-ntwrk/midnight-js-contracts';

const tx = await buildTransaction({
  contractAddress,
  circuitName: 'transfer',
  args: [recipient, amount],
  privateState,
});

// Sign and submit
const signedTx = await wallet.signTransaction(tx);
const txHash = await provider.submitTransaction(signedTx);

---

Wallet Integration

Browser Detection

declare global {
  interface Window {
    midnight?: {
      mnLace?: MidnightProvider;
    };
  }
}

function isWalletAvailable(): boolean {
  return typeof window !== 'undefined'
    && window.midnight?.mnLace !== undefined;
}

DApp Connector API

interface DAppConnectorAPI {
  enable(): Promise<MidnightAPI>;
  isEnabled(): Promise<boolean>;
  apiVersion(): string;
  name(): string;
  icon(): string;
}

async function connectWallet(): Promise<MidnightAPI> {
  if (!window.midnight?.mnLace) {
    throw new Error('Midnight Lace wallet not found');
  }
  return await window.midnight.mnLace.enable();
}

MidnightAPI Interface

interface MidnightAPI {
  getUsedAddresses(): Promise<string[]>;
  getBalance(): Promise<Balance>;
  signTx(tx: Transaction): Promise<SignedTransaction>;
  submitTx(signedTx: SignedTransaction): Promise<TxHash>;
  signData(address: string, payload: string): Promise<Signature>;
}

React Hook

export function useWallet() {
  const [state, setState] = useState({
    isConnected: false,
    address: null as string | null,
    isLoading: false,
    error: null as string | null,
  });

  const connect = useCallback(async () => {
    setState(prev => ({ ...prev, isLoading: true, error: null }));
    try {
      if (!window.midnight?.mnLace) {
        throw new Error('Please install Midnight Lace wallet');
      }
      const api = await window.midnight.mnLace.enable();
      const addresses = await api.getUsedAddresses();
      setState({
        isConnected: true,
        address: addresses[0] || null,
        isLoading: false,
        error: null,
      });
      return api;
    } catch (error) {
      setState(prev => ({
        ...prev,
        isLoading: false,
        error: error instanceof Error ? error.message : 'Failed',
      }));
      throw error;
    }
  }, []);

  return { ...state, connect };
}

Connection Flow

1. User clicks "Connect Wallet"
2. DApp calls window.midnight.mnLace.enable()
3. Wallet popup asks user to approve
4. User approves → DApp receives MidnightAPI
5. DApp can now interact with wallet

---

Error Handling

import { MidnightError, ContractError } from '@midnight-ntwrk/midnight-js-contracts';

try {
  await callContract({ ... });
} catch (error) {
  if (error instanceof ContractError) {
    console.error('Contract assertion failed:', error.message);
  } else if (error instanceof MidnightError) {
    console.error('Network error:', error.code);
  }
}

DApp Connector Errors

import { ErrorCodes } from '@midnight-ntwrk/dapp-connector-api';

// ErrorCodes.Rejected - User rejected the request
// ErrorCodes.InvalidRequest - Malformed transaction or request
// ErrorCodes.InternalError - DApp connector couldn't process request

try {
  const api = await window.midnight.mnLace.enable();
} catch (error) {
  if (error.code === ErrorCodes.Rejected) {
    console.log('User rejected wallet connection');
  }
}

ContractTypeError

// Thrown when there's a contract type mismatch
try {
  const contract = await findDeployedContract(provider, address, MyContract);
} catch (e) {
  if (e instanceof ContractTypeError) {
    console.error('Contract type mismatch:', e.circuitIds);
  }
}

---

Private State Witnesses

TypeScript witnesses implement the Compact witness declarations:

// counter-witnesses.ts
import type { Witnesses } from './managed/counter';

export type CounterPrivateState = {
  localSecretKey: Uint8Array;
  storedValues: Map<string, bigint>;
};

export const createWitnesses = (
  state: CounterPrivateState
): Witnesses<CounterPrivateState> => ({
  local_secret_key: () => state.localSecretKey,

  store_secret_value: (value: bigint) => {
    state.storedValues.set('secret', value);
    return undefined; // returns []
  },

  get_secret_value: () => {
    return state.storedValues.get('secret') ?? 0n;
  },
});

export const createInitialState = (): CounterPrivateState => ({
  localSecretKey: crypto.getRandomValues(new Uint8Array(32)),
  storedValues: new Map(),
});

---

Best Practices

1. Always check wallet availability before connecting
2. Handle user rejection gracefully
3. Store connection state in context/global state
4. Provide clear loading/error feedback
5. Test with Midnight Lace extension
6. Keep private state secure - never log or expose it

---

Rules

See /rules/ directory for detailed documentation:

• wallet-integration.md - Complete wallet integration patterns
• error-handling.md - Error handling best practices

---

References

• Midnight Docs
• TypeScript SDK
• DApp Connector API
• Lace Wallet