Svelte Adapter

The @presage-kit/svelte package provides Svelte stores and context helpers for building adaptive interfaces.

Installation

pnpm add @presage-kit/core @presage-kit/svelte

Context Setup

Use setAdaptiveClient() in your root layout to make the client available to all child components via Svelte’s context API.

src/routes/+layout.svelte

<script>
  import { setAdaptiveClient } from '@presage-kit/svelte'
  import { client } from '$lib/adaptive-client'

  setAdaptiveClient(client)
</script>

<slot />

useAdaptive() Store

The primary function for resolving adaptation points. Returns Svelte readable stores that update reactively when user context changes.

<script lang="ts">
  import { useAdaptive } from '@presage-kit/svelte'

  const { selectedVariant, resolution, context, track } = useAdaptive('onboarding', {
    variants: ['guided-tour', 'standard', 'minimal'] as const,
    defaultVariant: 'standard',
  })

  function handleComplete() {
    track('onboarding_completed')
  }
</script>

{#if $selectedVariant === 'guided-tour'}
  <h2>Welcome! Let us show you around.</h2>
  <button on:click={handleComplete}>Complete tour</button>
{:else if $selectedVariant === 'standard'}
  <h2>Welcome</h2>
{:else}
  <p>Good to see you again.</p>
{/if}

Parameters:

Param	Type	Description
adaptationId	string	Unique identifier for the adaptation point
config.variants	readonly string[]	Available variant IDs
config.defaultVariant	string	Fallback variant
config.strategy	Strategy	Optional. Defaults to { type: 'rules' }

Return type:

All reactive values are Svelte Readable stores — use the $ prefix to subscribe.

Field	Type	Description
selectedVariant	Readable<V>	The selected variant string
resolution	Readable<ResolvedAdaptation>	Full resolution details
context	Readable<UserContext>	Current user context
track	(event: string, properties?) => void	Scoped track function

Automatic impression tracking: useAdaptive() watches for variant changes and automatically tracks presage:impression events.

useVariant() Store

A lighter function that returns only the selected variant as a readable store.

<script lang="ts">
  import { useVariant } from '@presage-kit/svelte'

  const variant = useVariant('cta-style', {
    variants: ['primary', 'secondary', 'subtle'] as const,
    defaultVariant: 'primary',
  })
</script>

<button class="cta cta--{$variant}">Get Started</button>

Parameters: Same as useAdaptive().

Return type: Readable<V> — A store containing the selected variant string.

getAdaptiveClient()

Returns the AdaptiveClient instance from context. Use for imperative operations.

<script lang="ts">
  import { getAdaptiveClient } from '@presage-kit/svelte'

  const client = getAdaptiveClient()

  function handleExport() {
    client.track('feature_used', { featureId: 'export' })
  }
</script>

<button on:click={handleExport}>Export Data</button>

Throws an error if setAdaptiveClient() has not been called in a parent component.

Adaptive Navigation with evaluateAction()

Like the Vue adapter, the Svelte package does not ship a dedicated navigation component. Use evaluateAction() with a reactive declaration to reorder or hide navigation items.

<script lang="ts">
  import { getAdaptiveClient } from '@presage-kit/svelte'
  import { useAtom } from '@presage-kit/svelte'
  import { derived } from 'svelte/store'

  const client = getAdaptiveClient()

  const baseItems = [
    { id: 'home', label: 'Home', href: '/' },
    { id: 'analytics', label: 'Analytics', href: '/analytics' },
    { id: 'settings', label: 'Settings', href: '/settings' },
  ]

  const navItems = derived(useAtom(client.state), () => {
    const action = client.evaluateAction('sidebar-nav')

    if (action?.type === 'hide') return []

    if (action?.type === 'reorder') {
      const map = new Map(baseItems.map((item) => [item.id, item]))
      const ordered = action.order.filter((id) => map.has(id)).map((id) => map.get(id)!)
      const rest = baseItems.filter((i) => !action.order.includes(i.id))
      return [...ordered, ...rest]
    }

    return baseItems
  })
</script>

<nav>
  {#each $navItems as item (item.id)}
    <a href={item.href}>{item.label}</a>
  {/each}
</nav>

Tip

Wrap evaluateAction() in a derived() store that depends on the client state to get reactive updates.

Full Example: SaaS Dashboard

src/lib/adaptive-client.ts

import { createAdaptiveClient, createLocalStorageDriver } from '@presage-kit/core'

export const client = createAdaptiveClient({
  rules: [
    {
      id: 'power-user-sidebar',
      adaptationId: 'sidebar-nav',
      priority: 10,
      conditions: {
        all: [{ field: 'maturity', operator: 'eq', value: 'power' }],
      },
      action: { type: 'reorder', order: ['analytics', 'dashboards', 'settings', 'home'] },
    },
    {
      id: 'new-user-tour',
      adaptationId: 'onboarding',
      priority: 10,
      conditions: {
        all: [{ field: 'maturity', operator: 'eq', value: 'new' }],
      },
      action: { type: 'show', variantId: 'guided-tour' },
    },
    {
      id: 'experienced-skip',
      adaptationId: 'onboarding',
      priority: 5,
      conditions: {
        any: [
          { field: 'maturity', operator: 'eq', value: 'active' },
          { field: 'maturity', operator: 'eq', value: 'power' },
        ],
      },
      action: { type: 'show', variantId: 'minimal' },
    },
  ],
  persistence: {
    driver: createLocalStorageDriver('svelte-demo'),
  },
})

src/routes/+layout.svelte

<script>
  import { setAdaptiveClient } from '@presage-kit/svelte'
  import { client } from '$lib/adaptive-client'

  setAdaptiveClient(client)
</script>

<div class="layout">
  <SidebarNav />
  <main>
    <slot />
  </main>
</div>

src/lib/components/Onboarding.svelte

<script lang="ts">
  import { useAdaptive } from '@presage-kit/svelte'

  const { selectedVariant, track } = useAdaptive('onboarding', {
    variants: ['guided-tour', 'standard', 'minimal'] as const,
    defaultVariant: 'standard',
  })

  function handleComplete() {
    track('onboarding_completed')
  }
</script>

{#if $selectedVariant === 'guided-tour'}
  <div class="onboarding">
    <h2>Welcome! Let us show you around.</h2>
    <button on:click={handleComplete}>Complete Tour</button>
  </div>
{:else if $selectedVariant === 'standard'}
  <div class="onboarding">
    <h2>What is new</h2>
    <p>Check out the latest features.</p>
  </div>
{:else}
  <div class="onboarding">
    <p>Welcome back!</p>
  </div>
{/if}