Initializing state

To initialize on-chain state, use the init() method.

Like the constructor, init() is predefined on the base SmartContract class.

• It is called when you deploy your zkApp with the zkApp CLI for the first time.
• It is not called if you upgrade your contract and deploy a second time.

You can override this method to add initialization of your on-chain state:

class HelloWorld extends SmartContract {
  @state(Field) x = State<Field>();

  init() {
    super.init();
    this.x.set(Field(10)); // initial state
  }
}

You must call super.init() to set your entire state to 0.

If you don’t have any state to initialize to values other than 0, then there’s no need to override init(), you can just leave it out. The previous example set the state x to Field(10).

Try it out

Add the following Smart Contract:

class HelloWorld extends SmartContract {
  @state(Field) x = State<Field>();

  init() {
    super.init();
    this.x.set(Field(10));
  }
}

Add our local blockchain implementation so we can interact with our Smart Contract:

const Local = await Mina.LocalBlockchain({ proofsEnabled: false });
Mina.setActiveInstance(Local);

const deployerKey = Local.testAccounts[0].key;
const deployerAccount = deployerKey.toPublicKey();

const zkAppPrivateKey = PrivateKey.random();
const zkAppAddress = zkAppPrivateKey.toPublicKey();
const zkAppInstance = new HelloWorld(zkAppAddress);

Initialize the Smart Contract and deploy it:

const txn = await Mina.transaction(deployerAccount, async () => {
  AccountUpdate.fundNewAccount(deployerAccount);
  zkAppInstance.deploy();
});

await txn.prove();
await txn.sign([deployerKey, zkAppPrivateKey]).send();

Retrieve and log the initial state x:

const x = zkAppInstance.x.get();
Provable.log('state after init:', x)

Build and run the script in the terminal:

npm run build && node build/src/index.js

This will log the initial state of x which is set to 10 within the init() method:

state after init: 10