Where Logic Lives

Understanding where different kinds of logic should live is crucial to maintaining a clean architecture.

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❌ Anti-Pattern: Logic in View Layer

// BAD: View layer doing data orchestration
async function updateStatus(id, newStatus) {
  // View is managing cache invalidation
  const response = await fetch(`/api/invoices/${id}`, {
    method: 'PUT',
    body: JSON.stringify({ status: newStatus })
  })

  // View decides what to refetch
  await refetchInvoices()
  await refetchInvoice(id)

  // View coordinates multi-client sync
  broadcastToOtherTabs({ type: 'invoice-updated', id })
}

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✅ Good Pattern: Logic in Server + Verity

// GOOD: Server decides invalidation
// Backend (Python/Node/etc)
@app.put('/api/invoices/:id')
def update_invoice(id):
    invoice = update_status(id, request.json['status'])

    # Server authors the invalidation contract
    emit_directives([
        { 'op': 'refresh_item', 'name': 'invoice', 'id': id },
        { 'op': 'refresh_collection', 'name': 'invoices' }
    ])

    return { 'directives': [...] }

// Frontend (View Layer)
async function updateStatus(id, newStatus) {
    const res = await fetch(`/api/invoices/${id}`, {
        method: 'PUT',
        body: JSON.stringify({ status: newStatus })
    })
    const payload = await res.json()

    // Just forward directives to Verity
    await applyDirectives(payload.directives)
}

Why this is better: - Server decides what changed (domain knowledge) - Verity handles orchestration (data layer responsibility) - View just renders (presentation responsibility) - Multi-client sync is automatic (SSE fan-out)

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Summary

Verity is the backend of your frontend because it:

1. Sits between server and view (architectural layer)
2. Manages truth-state (not view-state)
3. Enforces separation of concerns (no mixing)
4. Provides a contract (directives, not ad-hoc)
5. Handles complexity (caching, staleness, concurrency, fan-out)
6. Stays protocol-agnostic (REST, GraphQL, gRPC—doesn't matter)
7. Stays framework-agnostic (thin adapters for Alpine, React, Vue, Svelte)

By extracting truth-state management into a dedicated layer, Verity lets servers focus on domain logic and views focus on rendering—each layer doing what it does best.