Invoke a contract function in a Stellar transaction using JavaScript

This is a simple example using the @stellar/stellar-sdk JavaScript library to create, simulate, and then assemble a Stellar transaction which invokes an increment function of the auth example contract.

(async () => {
  const {
    Keypair,
    Contract,
    SorobanRpc,
    TransactionBuilder,
    Networks,
    BASE_FEE,
  } = require("@stellar/stellar-sdk");

  // The source account will be used to sign and send the transaction.
  // GCWY3M4VRW4NXJRI7IVAU3CC7XOPN6PRBG6I5M7TAOQNKZXLT3KAH362
  const sourceKeypair = Keypair.fromSecret(
    "SCQN3XGRO65BHNSWLSHYIR4B65AHLDUQ7YLHGIWQ4677AZFRS77TCZRB",
  );

  // Configure SorobanClient to use the `soroban-rpc` instance of your
  // choosing.
  const server = new SorobanRpc.Server(
    "https://soroban-testnet.stellar.org:443",
  );

  // Here we will use a deployed instance of the `increment` example contract.
  const contractAddress =
    "CCTAMZGXBVCQJJCX64EVYTM6BKW5BXDI5PRCXTAYT6DVEDXKGS347HWU";
  const contract = new Contract(contractAddress);

  // Transactions require a valid sequence number (which varies from one
  // account to another). We fetch this sequence number from the RPC server.
  const sourceAccount = await server.getAccount(sourceKeypair.publicKey());

  // The transaction begins as pretty standard. The source account, minimum
  // fee, and network passphrase are provided.
  let builtTransaction = new TransactionBuilder(sourceAccount, {
    fee: BASE_FEE,
    networkPassphrase: Networks.FUTURENET,
  })
    // The invocation of the `increment` function of our contract is added
    // to the transaction. Note: `increment` doesn't require any parameters,
    // but many contract functions do. You would need to provide those here.
    .addOperation(contract.call("increment"))
    // This transaction will be valid for the next 30 seconds
    .setTimeout(30)
    .build();

  console.log(`builtTransaction=${builtTransaction.toXDR()}`);

  // We use the RPC server to "prepare" the transaction. This simulating the
  // transaction, discovering the storage footprint, and updating the
  // transaction to include that footprint. If you know the footprint ahead of
  // time, you could manually use `addFootprint` and skip this step.
  let preparedTransaction = await server.prepareTransaction(builtTransaction);

  // Sign the transaction with the source account's keypair.
  preparedTransaction.sign(sourceKeypair);

  // Let's see the base64-encoded XDR of the transaction we just built.
  console.log(
    `Signed prepared transaction XDR: ${preparedTransaction
      .toEnvelope()
      .toXDR("base64")}`,
  );

  // Submit the transaction to the Soroban-RPC server. The RPC server will
  // then submit the transaction into the network for us. Then we will have to
  // wait, polling `getTransaction` until the transaction completes.
  try {
    let sendResponse = await server.sendTransaction(preparedTransaction);
    console.log(`Sent transaction: ${JSON.stringify(sendResponse)}`);

    if (sendResponse.status === "PENDING") {
      let getResponse = await server.getTransaction(sendResponse.hash);
      // Poll `getTransaction` until the status is not "NOT_FOUND"
      while (getResponse.status === "NOT_FOUND") {
        console.log("Waiting for transaction confirmation...");
        // See if the transaction is complete
        getResponse = await server.getTransaction(sendResponse.hash);
        // Wait one second
        await new Promise((resolve) => setTimeout(resolve, 1000));
      }

      console.log(`getTransaction response: ${JSON.stringify(getResponse)}`);

      if (getResponse.status === "SUCCESS") {
        // Make sure the transaction's resultMetaXDR is not empty
        if (!getResponse.resultMetaXdr) {
          throw "Empty resultMetaXDR in getTransaction response";
        }
        // Find the return value from the contract and return it
        let transactionMeta = getResponse.resultMetaXdr;
        let returnValue = transactionMeta.v3().sorobanMeta().returnValue();
        console.log(`Transaction result: ${returnValue.value()}`);
      } else {
        throw `Transaction failed: ${getResponse.resultXdr}`;
      }
    } else {
      throw sendResponse.errorResultXdr;
    }
  } catch (err) {
    // Catch and report any errors we've thrown
    console.log("Sending transaction failed");
    console.log(JSON.stringify(err));
  }
})();