Interacting With Predicates

The Predicate class extends the Account class, inheriting all its methods. Therefore, there are multiple ways to interact with predicates, but broadly speaking, we can think about three:

• Checking Balances
• Transactions
• Transfers

Checking Balances

getBalances

This will return the balances of all assets owned by the predicate.

See also: Checking Wallet Balances

getResourcesToSpend

This will return the resources owned by a predicate so that they can be added to a transaction request.

This method is called under the hood when using transfer or createTransfer.

You may want to use this method when using a predicate in an existing transaction request.

import { bn, Provider, ScriptTransactionRequest, Wallet } from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../env';
import { ReturnTruePredicate } from '../../typegend';

const provider = await Provider.create(LOCAL_NETWORK_URL);
const funder = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);

const predicate = new ReturnTruePredicate({
  provider,
});

// Fund the predicate
const fundPredicate = await funder.transfer(
  predicate.address,
  100_000_000,
  provider.getBaseAssetId()
);
await fundPredicate.waitForResult();

// Instantiate the transaction request.
const transactionRequest = new ScriptTransactionRequest({
  gasLimit: 2000,
  maxFee: bn(0),
});

// Get the resources available to send from the predicate.
const predicateCoins = await predicate.getResourcesToSpend([
  { amount: 2000, assetId: provider.getBaseAssetId() },
]);

// Add the predicate input and resources.
transactionRequest.addResources(predicateCoins);

See code in context

Transactions

sendTransaction

This is used to send a transaction to the node.

import { bn, Provider, ScriptTransactionRequest, Wallet } from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../env';
import { ReturnTruePredicate } from '../../typegend';

const provider = await Provider.create(LOCAL_NETWORK_URL);
const funder = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);

const predicate = new ReturnTruePredicate({
  provider,
});

// Fund the predicate
const fundPredicate = await funder.transfer(
  predicate.address,
  100_000_000,
  provider.getBaseAssetId()
);
await fundPredicate.waitForResult();

// Instantiate the transaction request.
const transactionRequest = new ScriptTransactionRequest({
  gasLimit: 2000,
  maxFee: bn(100),
});

// Get the resources available to send from the predicate.
const predicateCoins = await predicate.getResourcesToSpend([
  { amount: 2000, assetId: provider.getBaseAssetId() },
]);

// Add the predicate input and resources.
transactionRequest.addResources(predicateCoins);

const txCost = await predicate.getTransactionCost(transactionRequest);

transactionRequest.gasLimit = txCost.gasUsed;
transactionRequest.maxFee = txCost.maxFee;

await predicate.fund(transactionRequest, txCost);

// Send the transaction using the predicate
const result = await predicate.sendTransaction(transactionRequest);

await result.waitForResult();

See code in context

---

simulateTransaction

You can use the simulateTransaction method to dry-run a predicate call without consuming resources. A typical use case of a dry-run call is to validate that sufficient funds are available to cover the transaction fees.

import {
  bn,
  Provider,
  ReceiptType,
  ScriptTransactionRequest,
  Wallet,
} from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../env';
import { ReturnTruePredicate } from '../../typegend';

const provider = await Provider.create(LOCAL_NETWORK_URL);
const funder = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);
const receiver = Wallet.generate({ provider });

const predicate = new ReturnTruePredicate({
  provider,
});

const fundPredicate = await funder.transfer(
  predicate.address,
  100_000_000,
  provider.getBaseAssetId()
);
await fundPredicate.waitForResult();

// Instantiate the transaction request.
const transactionRequest = new ScriptTransactionRequest({
  gasLimit: 2000,
  maxFee: bn(0),
});

transactionRequest.addCoinOutput(
  receiver.address,
  1000000,
  provider.getBaseAssetId()
);

const txCost = await predicate.getTransactionCost(transactionRequest);

transactionRequest.gasLimit = txCost.gasUsed;
transactionRequest.maxFee = txCost.maxFee;

await predicate.fund(transactionRequest, txCost);

const result = await predicate.simulateTransaction(transactionRequest);

See code in context

Transfers

createTransfer

The createTransfer method creates a transaction request with all the necessary transfer details. It automatically estimates the transaction costs via a dry-run call and funds the request with the required predicate resources. After this, one can submit the returned transaction request with greater certainty that it will succeed.

However, please remember that you can still modify the transfer request details and use its properties before submitting it to the node.

import { Provider, Wallet } from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../env';
import { ReturnTruePredicate } from '../../typegend';

const provider = await Provider.create(LOCAL_NETWORK_URL);
const funder = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);

const predicate = new ReturnTruePredicate({
  provider,
});

// Fund the predicate
const fundPredicate = await funder.transfer(
  predicate.address,
  100_000_000,
  provider.getBaseAssetId()
);
await fundPredicate.waitForResult();

const receiver = Wallet.generate({ provider });
const amountToReceiver = 1000;

const transactionRequest = await predicate.createTransfer(
  receiver.address,
  amountToReceiver,
  provider.getBaseAssetId(),
  {
    gasLimit: 1000,
  }
);

const sendFromPredicate = await predicate.sendTransaction(transactionRequest);

await sendFromPredicate.waitForResult();

See code in context

---

transfer

You can send funds to another address using the transfer method.

import { Provider, Wallet } from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../env';
import { ReturnTruePredicate } from '../../typegend';

const provider = await Provider.create(LOCAL_NETWORK_URL);
const funder = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);

const predicate = new ReturnTruePredicate({
  provider,
});

const fundPredicate = await funder.transfer(
  predicate.address,
  100_000_000,
  provider.getBaseAssetId()
);
await fundPredicate.waitForResult();

const receiver = Wallet.generate({ provider });
const amountToReceiver = 1000;

const transferPredicateCoins = await predicate.transfer(
  receiver.address,
  amountToReceiver,
  provider.getBaseAssetId(),
  {
    gasLimit: 1000,
  }
);

await transferPredicateCoins.waitForResult();

See code in context