Svelte Compare — Compare Svelte Files Online Free
Compare Svelte components across script, markup, and style in one view — reactive declarations included. Free, signup-free, components never uploaded.
How to Compare Svelte Files Online
Running a Svelte comparison in Svelte Compare is a three-step job:
- Add the original .svelte file in the original pane.
- Then paste the updated .svelte file into the second input.
- Click Compare and every difference is highlighted instantly.
Tip: give reactive-declaration highlights first attention — the $: statements rewire behavior with very little visible code. Compatible with all modern browsers — Chrome, Firefox, Edge, or Safari — on macOS, Windows, Linux, or mobile, and no usage limits apply. The side-by-side view is free and needs no login; the line-by-line and unified views come with Premium.
Understanding the Svelte File Format
Svelte (.svelte) files are single-file components for the Svelte framework, which compiles components to efficient vanilla JavaScript at build time. Each file combines a <script> block (with reactive declarations and stores), markup with Svelte's template syntax, and scoped <style> — three layers whose interactions make precise version comparison especially valuable. Single-file components bundle three languages into one file, and Svelte component comparison respects all three — a style edit, a template change, and a reactive-statement tweak are equally visible in one pass.
Common Uses of Svelte Files
Where teams actually use it, day to day:
- Teams diff page components across a SvelteKit major-version migration.
- Reviewers check reactive-statement changes that rewire behavior invisibly.
- Developers compare a component before and after extracting child components.
- Engineers audit store-related edits when state behaves unexpectedly.
- Maintainers verify a community PR changed only the targeted component.
- Teams document UI changes between release branches.
Diffing a page component across a SvelteKit major-version migration shows exactly which parts the migration guide actually touched.
Differences Detected in Svelte Files
The tool highlights Svelte's distinctive constructs: Svelte reactive declaration diff ($: statements added or changed), store subscription comparison ($store usage), Svelte action diff (use: directives), slot comparison for changed composition contracts, and lifecycle hook diff (onMount, onDestroy) — alongside template and scoped-style changes.
Examples of Changes Found in Svelte Files
Component changes the three-block diff typically picks up:
- A reactive statement '$: total = items.reduce(...)' changed to include a filter — an update-behavior change flagged on its line.
- A component where 'export let value' gained a default and a new 'export let disabled = false' prop appeared.
- A template where an {#each} block gained a keyed expression (item.id), changing list reconciliation.
- A scoped style where the .active class's transition timing changed from 150ms to 300ms.
- A component where $: total = price * qty became $: total = subtotal — one reactive dependency swap that froze the displayed total until unrelated state changed.
Why Use FileDiffs for Svelte Comparison
A Svelte component packs script, markup, and style into one file, and its reactivity hides in a dollar sign, so a changed reactive statement rewires behavior with almost no visible code. FileDiffs reviews all three layers in one pass, comparing components in the browser with nothing uploaded. It's built for real SvelteKit work, migrations and refactors, with examples like a reactive total losing the dependency that drove it and freezing on screen until unrelated state happens to change.
Frequently Asked Questions About Compare Svelte Files Online
Upload both .svelte files and the tool highlights changes across script, markup, and style blocks in one side-by-side view. Script, markup, and style blocks are reviewed in one pass — all three layers of the component in a single view.
Compare the component across versions; changed props, reactive statements, template blocks, and styles are each flagged at their lines for structured review. Reactive declaration highlights come first: the $: statements rewire behavior with very little visible code.
Diff it against the previous version, prioritizing $: reactive declarations and prop changes — the edits most likely to alter component behavior. Store subscription edits are small in text but change data flow throughout the component.
They diff as text, which is mainly useful during a migration: compare the ported component against the original to verify logic and template parity. Both are single-file components, so the comparison maps cleanly section by section during a framework migration.
Diff each changed component against its base and review highlights by block: props and reactivity first, template structure second, scoped styles last. Diffing a page component across a SvelteKit version migration shows which parts the upgrade actually touched.
Yes. Your components are compared in the browser with nothing uploaded, so private UI code stays confidential. The comparison runs on your device and leaves no trace. You can verify this yourself in your browser's network tab.