Examples

An extensive collection of examples is available in the GitLab repository. Below we discuss a few of these examples in more details. These examples focus mainly on the use of the SDK, while the Examples page in the language section focuses more on the NexScript syntax.

Transfer With Timeout

The idea of this smart contract is explained on the Language Examples page. The gist is that it allows you to send an amount of NEXA to someone, but if they don't claim the sent amount, it can be recovered by the sender.

TransferWithTimeout.nex

contract TransferWithTimeout(pubkey sender, pubkey recipient, int timeout) {
    function transfer(sig recipientSig) {
        require(checkSig(recipientSig, recipient));
    }

    function timeout(sig senderSig) {
        require(checkSig(senderSig, sender));
        require(tx.time >= timeout);
    }
}

Now to put this smart contract in use in a JavaScript application we have to use the NexScript SDK in combination with a Nexa library such as libnexa-ts. This library is used to generate public/private keys for the contract participants: a libnexa-ts PrivateKey (or its WIF string) is passed to SignatureTemplate, and the public key bytes (privateKey.publicKey.toBuffer()) are passed as pubkey arguments. The key generation code is left out of this example.

TransferWithTimeout.js

import { Contract, SignatureTemplate } from '@nexscript/nexscript';
import { alicePriv, alicePub, bobPriv, bobPub } from './somewhere.js';
import artifact from './transfer_with_timeout.json';

// Instantiate a new contract using the artifact and constructor arguments:
// { sender: alicePub, recipient: bobPub, timeout: 1000000 }
// No network provider is provided, so the default ElectrumNetworkProvider is used
// (for the network in the NETWORK environment variable, or regtest)
const contract = new Contract(artifact, [alicePub, bobPub, 1000000n]);

// Display contract address and balance
console.log('contract address:', contract.address);
console.log('contract balance:', await contract.getBalance());

// Call the transfer function with Bob's signature
// i.e. Bob claims the money that Alice has sent him
const txDetails = await contract.functions
  .transfer(new SignatureTemplate(bobPriv))
  .to('nexa:nqtsq5g537fcf6z85pgwk4my5e5ddmypa2sm47mkzavt6zky', 10000n)
  .send();
console.log(txDetails);

// Call the timeout function with Alice's signature
// i.e. Alice recovers the money that Bob has not claimed
// But because the timeout has not passed yet, the function fails and
// we call the meep function so the transaction can be debugged instead
const meepStr = await contract.functions
  .timeout(new SignatureTemplate(alicePriv))
  .to('nexa:nqtsq5g5wtkt44pfqusjj3wulk2n2pd27lhpzg0m326kcnsj', 10000n)
  .meep();
console.log(meepStr);