Best practices

State management

Manage checkout state carefully to avoid re-initialization and stale data. Keep configuration objects stable and observe state changes with lifecycle-aware collectors.

Web
Android
iOS

Define options outside functions

Create options objects once and reuse them to avoid unnecessary re-initialization:

Define static options outside your function scope. The SDK uses deep comparison to detect actual changes, but stable object references reduce comparison overhead and improve performance.

// ✅ GOOD: Created once
const SDK_OPTIONS = {
  locale: 'en-GB',
};

function initCheckout() {
  const checkout = document.querySelector('primer-checkout');
  checkout.options = SDK_OPTIONS; // Same reference every time
}

// ❌ AVOID: Created every time function runs
function initCheckout() {
  const checkout = document.querySelector('primer-checkout');
  checkout.options = { locale: 'en-GB' }; // New object every execution
}

The SDK performs deep comparison to detect actual changes in the options object. Using stable references (the GOOD pattern above) minimizes comparison overhead and remains the recommended best practice for optimal performance.

Use lifecycle-aware state collection

Always use collectAsStateWithLifecycle() instead of collectAsState() to prevent unnecessary work when the app is in the background:

val state by checkout.state.collectAsStateWithLifecycle()

Avoid wrapping the controller in a ViewModel

The checkout controller is already a ViewModel internally. Don’t wrap it in another ViewModel unless you need to coordinate with other app state.

Define settings and theme as constants

Create PrimerSettings and PrimerCheckoutTheme outside your view body to avoid unnecessary re-creation on each SwiftUI render cycle:

SwiftUI re-evaluates body frequently. Defining configuration objects as constants ensures they are created once and reused.

// ✅ GOOD: Created once
private let primerSettings = PrimerSettings(paymentHandling: .auto)
private let primerTheme = PrimerCheckoutTheme(
  colors: ColorOverrides(primerColorBrand: .blue)
)

struct CheckoutView: View {
  let clientToken: String

  var body: some View {
    PrimerCheckout(
      clientToken: clientToken,
      primerSettings: primerSettings,
      primerTheme: primerTheme
    )
  }
}

// ❌ AVOID: Created every render
struct CheckoutView: View {
  let clientToken: String

  var body: some View {
    PrimerCheckout(
      clientToken: clientToken,
      primerSettings: PrimerSettings(paymentHandling: .auto),
      primerTheme: PrimerCheckoutTheme(colors: ColorOverrides(primerColorBrand: .blue))
    )
  }
}

Use proper @State management

When storing checkout-related values in SwiftUI state, use @State for simple values and @StateObject for observable objects:

struct CheckoutView: View {
  let clientToken: String
  @State private var paymentCompleted = false
  @State private var paymentResult: PaymentResult?

  var body: some View {
    if paymentCompleted, let result = paymentResult {
      ConfirmationView(result: result)
    } else {
      PrimerCheckout(
        clientToken: clientToken,
        onCompletion: { state in
          if case .success(let result) = state {
            paymentResult = result
            paymentCompleted = true
          }
        }
      )
    }
  }
}

Observe state through the session, not callbacks

For composable, inline checkout, hold a PrimerCheckoutSession as a @StateObject and observe its @Published properties. The session is automatically started on appear and torn down on disappear by the .primerCheckoutSession(_:onCompletion:) modifier — you don’t manage an AsyncStream or a manual Task:

struct CheckoutView: View {
  @StateObject private var session: PrimerCheckoutSession

  init(clientToken: String) {
    _session = StateObject(
      wrappedValue: PrimerCheckoutSession(clientToken: clientToken)
    )
  }

  var body: some View {
    ScrollView {
      PrimerCardForm()
    }
    .primerCheckoutSession(session) { state in
      // ✅ Terminal outcome delivered exactly once
      handleStateChange(state)
    }
  }
}

The terminal PrimerCheckoutState arrives through onCompletion, while the session’s phase and the per-feature sessions (cardForm, selection) drive your custom slots reactively as @Published properties.

Error handling

Log diagnostics IDs and handle failures gracefully. Every error from the SDK includes identifiers that help Primer support diagnose issues.

Web
Android
iOS

Monitor SDK initialization

checkout.addEventListener('primer:ready', (event) => {
  const primer = event.detail;
  console.log('SDK initialized');
  console.log('Applied locale:', checkout.options?.locale);
  console.log('Active payment methods:', primer.getPaymentMethods?.());
});

Debug configuration issues

Common debugging approaches for options-related issues:

When options aren’t working as expected, check these common issues first:

Check object reference stability:

const options = { locale: 'en-GB' };
console.log('Options reference:', options);

// Later in code
checkout.options = options;
console.log('Applied options:', checkout.options);
console.log('References match:', checkout.options === options);

Verify component properties vs SDK options:

// Component properties use setAttribute()
const checkout = document.querySelector('primer-checkout');

checkout.setAttribute('client-token', 'new-token');
console.log('Token attribute:', checkout.getAttribute('client-token'));

// SDK options use direct property assignment
checkout.options = { locale: 'en-GB' };
console.log('Options object:', checkout.options);

Always handle outcomes

The Android Components SDK always uses AUTO mode — there is no manual mode. Even with default screens, observe checkout.state for logging and analytics:

val state by checkout.state.collectAsStateWithLifecycle()

LaunchedEffect(state) {
    when (val s = state) {
        is PrimerCheckoutState.Success -> {
            analytics.trackPurchase(s.checkoutData)
        }
        is PrimerCheckoutState.Failure -> {
            analytics.trackError(s.error.diagnosticsId)
        }
        else -> Unit
    }
}

PrimerCheckoutSheet(checkout = checkout)

Log diagnostics IDs

Every PrimerError includes a diagnosticsId. Log it for troubleshooting with Primer support:

is PrimerCheckoutState.Failure -> {
    Log.e("Checkout", "Error: ${s.error.diagnosticsId}")
}

Handle all completion states

Always handle all cases in the onCompletion callback to avoid unexpected behavior:

PrimerCheckout(
  clientToken: clientToken,
  onCompletion: { state in
    switch state {
    case .success(let result):
      handleSuccess(result)
    case .failure(let error):
      handleFailure(error)
    case .dismissed:
      handleDismissal()
    case .initializing, .ready:
      break
    }
  }
)

Not handling the .dismissed case can leave your app in an inconsistent state if the user swipes to dismiss the checkout.

Log diagnostics IDs

Every error includes a diagnosticsId. Log it for troubleshooting with Primer support, and use recoverySuggestion for user-facing messages:

case .failure(let error):
  print("Error diagnosticsId: \(error.diagnosticsId)")
  if let suggestion = error.recoverySuggestion {
    showUserMessage(suggestion)
  }

Performance

Minimize unnecessary re-renders and keep configuration stable. Initialize the SDK as early as possible so it can prefetch configuration while the user navigates.

Web
Android
iOS

Use TypeScript interfaces for type safety

Define TypeScript interfaces for your options objects to catch errors at compile time:

interface PrimerSDKOptions {
  locale: string;
  paymentMethodOptions?: {
    PAYMENT_CARD?: {
      requireCVV?: boolean;
      requireBillingAddress?: boolean;
    };
    APPLE_PAY?: {
      merchantName?: string;
      merchantCountryCode?: string;
    };
  };
}

const options: PrimerSDKOptions = {
  locale: 'en-GB',
  paymentMethodOptions: {
    PAYMENT_CARD: {
      requireCVV: true,
      requireBillingAddress: true,
    },
  },
};

Test options configuration separately

Create isolated tests for your options configuration:

describe('SDK Options Configuration', () => {
  it('should create valid options object', () => {
    const options = {
      locale: 'en-GB',
    };

    expect(options.locale).toBe('en-GB');
  });

  it('should maintain stable reference', () => {
    const options = { locale: 'en-GB' };
    const checkout = document.querySelector('primer-checkout');
    checkout.options = options;

    expect(checkout.options).toBe(options); // Same reference
  });
});

Initialize early

Create the checkout controller as early as possible so the SDK can fetch configuration while the user navigates to checkout:

@Composable
fun CheckoutScreen(clientToken: String) {
    val checkout = rememberPrimerCheckoutController(clientToken)
    // SDK starts loading immediately
}

Avoid recreating the controller

rememberPrimerCheckoutController survives recomposition. Don’t call it conditionally or inside callbacks.

Avoid creating objects in SwiftUI `body`

Define PrimerSettings and PrimerCheckoutTheme as constants outside the view body. SwiftUI re-evaluates body frequently, so inline allocations waste resources:

// ✅ GOOD: Defined once outside body
private let primerSettings = PrimerSettings(paymentHandling: .auto)

struct CheckoutView: View {
  let clientToken: String

  var body: some View {
    PrimerCheckout(
      clientToken: clientToken,
      primerSettings: primerSettings
    )
  }
}

Let the session own its lifecycle

For composable checkout, hold the PrimerCheckoutSession as a @StateObject and attach the .primerCheckoutSession(_:onCompletion:) modifier. The modifier starts the session on appear and tears it down on disappear, so you never manage a manual Task or AsyncStream:

struct CheckoutView: View {
  @StateObject private var session: PrimerCheckoutSession

  init(clientToken: String) {
    _session = StateObject(
      wrappedValue: PrimerCheckoutSession(clientToken: clientToken)
    )
  }

  var body: some View {
    ScrollView {
      PrimerCardForm()
    }
    .primerCheckoutSession(session) { state in
      handleStateChange(state)
    }
  }
}

Don’t retain self in `onCompletion`

The completion closure can outlive the view that created it. When forwarding the terminal state to a long-lived object such as a view model, capture it weakly to avoid retain cycles:

.primerCheckoutSession(session) { [weak viewModel] state in
  Task { await viewModel?.handleState(state) }
}

Security

Never expose API keys in client code. Keep configuration minimal and handle sensitive data on your server.

Web
Android
iOS

Distinguish between component properties and SDK options

Component Properties are HTML attributes that configure the component container. SDK Options are configuration settings for the SDK itself.

Mixing these up will cause silent failures. Component properties must use setAttribute(). SDK options must be assigned directly to .options.

Component Properties (use setAttribute()):

client-token - API authentication
custom-styles - Visual theming
loader-disabled - Loader behavior

SDK Options (use options object):

locale - UI language
Payment method configuration
Feature settings
Merchant domain and API settings

// ✅ CORRECT: Clear separation
const checkout = document.querySelector('primer-checkout');

// Component properties
checkout.setAttribute('client-token', 'your-token');
checkout.setAttribute('loader-disabled', 'false');

// SDK options
checkout.options = {
  locale: 'en-GB',
  applePay: { buttonType: 'buy' },
};

// ❌ WRONG: Mixing them up
checkout.setAttribute('locale', 'en-GB'); // Won't work - locale is an SDK option
checkout.options = {
  clientToken: 'your-token', // Wrong - this is a component property
};

Keep options simple and focused

Only configure what you need:

// ✅ GOOD: Simple, focused configuration
checkout.options = {
  locale: 'en-GB',
};

// ❌ AVOID: Over-configuration with unused options
checkout.options = {
  locale: 'en-GB',
  paymentMethodOptions: {
    PAYMENT_CARD: {
      requireCVV: true,
      requireBillingAddress: false,
      // ... 20 more unused options
    },
    APPLE_PAY: {
      // ... configured but not used
    },
  },
};

Client token handling

Generate client tokens on your server, never hardcode them
Client tokens are single-use and expire — generate a fresh one for each checkout session
Never log or persist client tokens

Keep configuration minimal

Only configure what you need in PrimerSettings. The SDK ships with sensible defaults:

// ✅ GOOD: Only override what you need
private let primerSettings = PrimerSettings(paymentHandling: .auto)

// ❌ AVOID: Over-configuration with defaults
private let primerSettings = PrimerSettings(
  paymentHandling: .auto,
  localeData: nil,
  uiOptions: nil
)

Testing

Use sandbox mode with test cards to verify your integration before going to production.

Web
Android
iOS

Test your checkout in a sandbox environment. Verify that:

Options are applied correctly
Events fire as expected
Error handling works for declined cards
All payment methods render properly

Use sandbox environment

Always test with sandbox client tokens before going to production. Use test card numbers:

Card	Result
`4111 1111 1111 1111`	Success
`4000 0000 0000 0002`	Declined

Test dark mode

Verify your custom theme looks correct in both light and dark modes:

// Force dark mode for testing
val theme = PrimerTheme(
    darkColorTokens = object : DarkColorTokens() {
        override val primerColorBrand: Color = Color(0xFFA29BFE)
    },
)

Accessibility

The SDK supports TalkBack and other accessibility services. Default components include:

Content descriptions for all interactive elements
Semantic roles (buttons, inputs, headings)
Focus management for screen transitions

When building custom layouts, ensure your custom components also include accessibility annotations:

Modifier.semantics {
    contentDescription = "Pay with Visa ending in 4242"
    role = Role.Button
}

Use sandbox environment

Always test with sandbox client tokens before going to production. Use test card numbers:

Card	Result
`4111 1111 1111 1111`	Success
`4000 0000 0000 0002`	Declined

Use the Primer Dashboard to configure test payment methods.

Test dark mode

Verify your custom theme looks correct in both light and dark modes using the iOS simulator’s appearance settings or by overriding the color scheme in your preview:

#Preview {
  CheckoutView(clientToken: "sandbox-token")
    .preferredColorScheme(.dark)
}

Accessibility

The SDK supports VoiceOver and other iOS accessibility services. Default components include:

Accessibility labels for all interactive elements
Trait annotations (button, header, text field)
Focus management for screen transitions

When building custom layouts, ensure your custom components include accessibility modifiers:

Text("Pay with Visa ending in 4242")
  .accessibilityLabel("Pay with Visa ending in 4242")
  .accessibilityAddTraits(.isButton)

​State management

​Define options outside functions

​Use lifecycle-aware state collection

​Avoid wrapping the controller in a ViewModel

​Define settings and theme as constants

​Use proper @State management

​Observe state through the session, not callbacks

​Error handling

​Monitor SDK initialization

​Debug configuration issues

​Always handle outcomes

​Log diagnostics IDs

​Handle all completion states

​Log diagnostics IDs

​Performance

​Use TypeScript interfaces for type safety

​Test options configuration separately

​Initialize early

​Avoid recreating the controller

​Avoid creating objects in SwiftUI body

​Let the session own its lifecycle

​Don’t retain self in onCompletion

​Security

​Distinguish between component properties and SDK options

​Keep options simple and focused

​Client token handling

​ProGuard

​Client token handling

​Keep configuration minimal

​Testing

​Use sandbox environment

​Test dark mode

​Accessibility

​Use sandbox environment

​Test dark mode

​Accessibility

State management

Define options outside functions

Use lifecycle-aware state collection

Avoid wrapping the controller in a ViewModel

Define settings and theme as constants

Use proper @State management

Observe state through the session, not callbacks

Error handling

Monitor SDK initialization

Debug configuration issues

Always handle outcomes

Log diagnostics IDs

Handle all completion states

Log diagnostics IDs

Performance

Use TypeScript interfaces for type safety

Test options configuration separately

Initialize early

Avoid recreating the controller

Avoid creating objects in SwiftUI `body`

Let the session own its lifecycle

Don’t retain self in `onCompletion`

Security

Distinguish between component properties and SDK options

Keep options simple and focused

Client token handling

ProGuard

Client token handling

Keep configuration minimal

Testing

Use sandbox environment

Test dark mode

Accessibility

Use sandbox environment

Test dark mode

Accessibility