Svelte & SvelteKit

Why Svelte

Svelte takes a radically different approach to building user interfaces. Instead of shipping a runtime that interprets your components in the browser, Svelte compiles them into vanilla JavaScript at build time. The framework disappears before your code reaches users.

This compilation approach delivers tangible benefits. Bundle sizes shrink dramatically. A typical Svelte application ships 30-50% less JavaScript than React or Vue equivalents. Less code means faster downloads, especially on mobile networks. Less code means faster parsing. Less code means your application starts faster.

The developer experience is equally compelling. Svelte components look like HTML with superpowers. Reactivity is built into the language with simple assignments. No useState hooks. No reactive() wrappers. Change a variable, the UI updates. The syntax feels obvious in a way that frameworks with heavier abstractions don’t achieve.

What We Build

Performance-critical marketing sites showcase Svelte’s strengths. Landing pages that compete for attention need to load instantly. We’ve built sites that score 100 on Lighthouse performance metrics. Not through heroic optimization, but through Svelte’s default output being so efficient.

Interactive web applications benefit from Svelte’s approach to reactivity. Data flows through the component tree predictably. Updates happen precisely where needed — no wasted re-renders. We’ve built complex forms that validate in real-time, drag-and-drop interfaces that respond instantly, and search experiences that filter thousands of items without stuttering.

Embeddable widgets demand minimal footprint. A 10KB widget won’t slow down the host page. A 200KB widget will. Svelte lets us build rich functionality in tiny bundles. We’ve shipped embeddable components for customer surveys, comment systems, and interactive calculators — all under 15KB gzipped.

Progressive web apps leverage SvelteKit’s offline capabilities. Service workers cache intelligently. The app shell loads from cache while fresh data streams in. Users on spotty connections stay productive. The install experience is smooth because the payload is small.

Tools for developers and power users often run in constrained environments. Browser extensions have size limits. Bookmarklets need to be tiny. Embedded webviews have memory constraints. Svelte’s compile-time approach makes these projects feasible where other frameworks would struggle.

Our Experience Level

We’ve built production Svelte applications since version 3. We’ve migrated to Svelte 4 and now Svelte 5. The runes syntax in Svelte 5 represents a significant evolution — we understand both the old and new patterns.

SvelteKit has been our full-stack framework of choice for Svelte projects since its 1.0 release. We’ve deployed to Vercel, Cloudflare Pages, Netlify, and traditional Node servers. Each adapter has quirks; we know them.

Our pattern library includes: stores for shared state, derived stores for computed values, readable stores for external data sources, custom store factories for reusable logic. We’ve built component libraries with proper type definitions. We’ve integrated Svelte with D3 for complex visualizations. We’ve handled authentication, authorization, and multi-tenant architectures.

Form handling in SvelteKit deserves special mention. Server actions enable progressive enhancement — forms work without JavaScript, then get enhanced with client-side interactivity. We use this pattern extensively for accessible, resilient applications.

When to Use Svelte

Choose Svelte when bundle size directly impacts your business. Mobile audiences on 3G connections. Emerging markets where data is expensive. Embedded contexts with strict size budgets. Performance benchmarks your competitors can’t match.

Choose Svelte when developer experience matters. Teams frustrated with framework complexity find Svelte refreshing. The learning curve is gentle. The syntax is intuitive. New developers contribute quickly. Existing developers enjoy writing code more.

Choose Svelte when you want progressive enhancement to be practical. SvelteKit makes it easy to build applications that work without JavaScript and get better with it. Server rendering handles the initial load. Form actions handle submissions. Client-side code adds polish, not requirements.

Choose Svelte when you value explicitness. Reactivity is visible in the code. There’s no magic updating happening behind the scenes. When something breaks, the cause is usually clear.

Don’t choose Svelte if you need the largest possible ecosystem. React has more component libraries, more integrations, more Stack Overflow answers. Don’t choose Svelte if your hiring depends on finding developers with existing framework experience — the Svelte talent pool is smaller. Don’t choose Svelte for projects where your team has deep investment in React or Vue tooling and patterns. Migration costs are real.

Common Challenges and How We Solve Them

Ecosystem gaps require creative solutions. Sometimes the perfect React component doesn’t have a Svelte equivalent. We evaluate alternatives: Can we use a vanilla JavaScript library? Can we build a simpler custom component? Can we wrap the React component with a compatibility layer? Usually the simpler solution is better anyway.

Svelte 5 migration requires attention. The runes syntax ($state, $derived, $effect) replaces the previous reactive paradigm. Existing codebases need updates. We approach this incrementally — new components use runes, existing components migrate as they’re modified. The compiler helps catch issues.

TypeScript integration is excellent in modern Svelte, but requires proper configuration. We use strict mode. We type props explicitly. We generate types for SvelteKit’s load functions and form actions. The investment in types pays off in fewer runtime errors and better editor support.

State management at scale needs structure. Svelte stores are powerful but can become scattered. We organize stores by domain. We use derived stores to compute values rather than duplicating logic. We keep store interactions predictable by establishing clear patterns for the team.

Testing Svelte components uses familiar tools with some Svelte-specific setup. Vitest with @testing-library/svelte handles most needs. We test user interactions, not implementation details. We verify that clicking a button produces the expected result. We check that forms validate correctly. The tests remain stable through refactors because they mirror how users interact with the application.

Server-side rendering edge cases appear in every framework. Browser APIs accessed during SSR. Timing differences between server and client. We address these with environment checks, dynamic imports, and SvelteKit’s browser detection. The patterns are documented and consistent across our projects.