Svelte 5: A Quick Guide from Basics to Deployment

Source: Dev.to

According to The State of JavaScript 2024 survey, Svelte’s adoption has been steadily growing since 2020, gaining increasing attention in the developer community. While React and Vue remain the dominant choices, Svelte is moving from niche to mainstream, becoming a significant force in the frontend ecosystem.

If you haven’t tried Svelte yet, this article gives a quick overview of its core concepts, advantages, and how to get started.

What is Svelte? How is it Different from React/Vue?

Svelte is a frontend component framework for building user interfaces, just like React and Vue. The fundamental difference is that Svelte is a compile‑time framework, while React and Vue are runtime frameworks.

Runtime vs. Compile‑time

• React/Vue – You write a “recipe”, and the framework “cooks the meal” in the user’s browser (virtual DOM diffing, etc.).
• Svelte – The meal is already cooked on your machine; users get the “finished dish”. Svelte compiles your components into efficient vanilla JavaScript during the build phase, so there is no Svelte runtime in the final bundle.

Comparison

Advantages and Use Cases

Advantages

1. Smaller Bundle Size
   No runtime means smaller bundles. A simple Svelte app might be only a few KB, while an equivalent React app needs 40 KB+ just for the framework.

2. Better Performance
   Without virtual DOM diffing overhead, Svelte directly manipulates the real DOM. In scenarios with many node updates, Svelte is typically faster than React/Vue.

3. Clean Syntax

   let count = $state(0);
   <button on:click={() => count++}>
     Clicked {count} times
   </button>

   No useState, no ref. HTML, CSS, and JS live in a single .svelte file with a clear structure.

4. Low Learning Curve
   If you’re familiar with HTML, CSS, and JavaScript, picking up Svelte is quick. There’s no JSX mental overhead, and you don’t need to learn rules like “hooks can’t be inside conditionals”.

Good Use Cases

• Personal projects / Small apps – Fast development, less code.
• Performance and size‑sensitive scenarios – Embedded widgets, mobile H5, low‑bandwidth environments.
• Teams wanting to try new tech – Svelte’s developer experience is genuinely great.
• Static websites / Blogs – Combined with SvelteKit, you can easily generate static sites.

Less Ideal Scenarios

• Teams already deeply invested in React/Vue with heavy ecosystem dependencies.
• Projects requiring extensive third‑party component libraries (Svelte’s ecosystem is still smaller than React’s).

Svelte 5: Runes Make Reactivity More Intuitive

Svelte 5 was officially released in October 2024. The biggest change is the introduction of the Runes system, which makes reactive state declarations explicit.

The Old “Implicit Magic”

let count = 0;           // Automatically becomes reactive
$: doubled = count * 2;  // Automatically tracks dependencies

The $: syntax can be confusing, and it’s not obvious which variables are reactive.

Svelte 5’s Explicit Declarations

let count = $state(0);               // Reactive state
let doubled = $derived(count * 2);   // Derived value

<button on:click={() => count++}>
  {count} × 2 = {doubled}
</button>

• $state() → reactive variable
• $derived() → computed value (like Vue’s computed)

Common Runes

Why This Is More Beginner‑Friendly

• No guessing – $state clearly marks reactive variables.
• Consistent syntax – Same declaration style works at the top level or inside functions.
• Easier debugging – It’s obvious which piece of state caused a break.

If you’ve used React Hooks or Vue 3’s Composition API, Runes feel familiar but with cleaner syntax and fewer rules.

SvelteKit Overview

If Svelte is for writing components, SvelteKit is for building complete applications. Its relationship to Svelte is similar to Next.js ↔ React or Nuxt ↔ Vue.

What Does SvelteKit Provide?

1. File‑based Routing
   Create folders and files under src/routes; routes are generated automatically.

   src/routes/
   ├── +page.svelte          → /
   ├── about/
   │   └── +page.svelte      → /about
   └── blog/
       └── [slug]/
           └── +page.svelte → /blog/:slug

2. Multiple Rendering Modes

   • SSR – Server‑Side Rendering (SEO‑friendly).
   • CSR – Client‑Side Rendering (pure frontend).
   • SSG – Static Site Generation (HTML at build time).
   • Hybrid – Different pages can use different strategies.

3. Data Loading
   Each route can have a +page.js (or +page.server.js) to load data before rendering.

   // src/routes/blog/+page.server.js
   export async function load() {
     const posts = await db.getPosts();
     return { posts };
   }

   <script>
     let { data } = $props();
   </script>
   
   {#each data.posts as post}
     <h2>{post.title}</h2>
   {/each}

4. Adapters
   SvelteKit can deploy to various platforms by switching adapters, allowing the same codebase to run on Vercel, Netlify, Cloudflare Workers, Node.js, and more.