> ## Documentation Index
> Fetch the complete documentation index at: https://docs.streambird.io/llms.txt
> Use this file to discover all available pages before exploring further.

# SDK Callback vs Promise

We provide you the flexibility to use either approache when signing in to verify.

## Callback

With this approach, the callbacks for onSuccess and onError can be handled in the initialization process of the SDK. This is a valid approach if you are using the default SDK UI component.

```javascript callbacks Example theme={null}
var sdk = MoonKey('pk_test_KJuRUZmh1XC342h1n39gH84MuSZDyD13NfhtDkaY6IfwpQA0H', {
  headless: false,
  networkConfig: {
    rpcUrl: 'https://goerli.infura.io/v3/INFURA_API_KEY'
  }
});

sdk.init(
  ...
  callbacks: {
    onSuccess: async (data) => {
      console.log("callback onSuccess", data)
      const isLogged = await sdk.sessions.isLoggedIn()
      console.log('isLogged:', isLogged)
      const accounts = await sdk.rpcProvider.send('eth_accounts', [])
      console.log('Iframe accounts:', { accounts })
      const user = await sdk.users.getCurrentUser()
      console.log('User:', user)
    },
    onError: (data) => {
      console.log("callback onError", data);
    }
  }
)
```

## Promise

You may have designed your own login UI and need to hook up the login / sign in button event. This will not be possible with the callbacks approach so we have provided a `promise` approach.

```javascript Promise Example theme={null}
  var sdk = MoonKey('pk_test_KJuRUZmh1XC342h1n39gH84MuSZDyD13NfhtDkaY6IfwpQA0H', {
    headless: false,
    networkConfig: {
      rpcUrl: 'https://goerli.infura.io/v3/INFURA_API_KEY'
    }
  });

  sdk.init(...);

  const handleLogin = async (e) => {
    e.preventDefault();

    const email = new FormData(e.target).get("email");
    console.log('email', email);

    if(email) {
      try {
        let result = await sdk.magicLinks.loginOrCreate(email);
        console.log('result from sdk-constructor', result);
        const rpcProvider = sdk.rpcProvider
        localStorage.setItem('rpc', rpcProvider)
        console.log('RpcProvider: ', rpcProvider)
      } catch(error) {
        console.log('error', error);
      }
    }
  };
```

With the above code you initialize the `sdk` and then use the `sdk` to login when you press the button and use `await` to wait for the authentication login response.