wcb vs Lit vs FAST: size and feature comparison

The releases since v5 gave the WebComponent base class a stricter compliance with custom elements specifications, quality of life improvements, and overall robustness by combining JS components authoring expectations and stable HTML behaviors. We now have in-place re-rendering, HTML boolean semantics and overrideable attribute converters, among other improvements.

This page puts these benefits and their cost in context: how much does WCB weigh in size compared to similar web-component libraries, what does each library buy you over writing custom elements from scratch, and when is WCB the right choice.

Measured size: the same component in each library

Numbers below are measured from the same minimal counter component (one reactive count prop, a click handler, a re-render on change) written in each library, bundled with esbuild --bundle --minify --format=esm, and compressed with gzip (level 9) and brotli (quality 11). This is the real “cost of your first component”: library runtime + component code, everything the browser downloads.

See it live: Library comparison demo ↗ — every counter running side by side, the source of each, and the measure.mjs script that produces the table below.

Library	Version	Minified	Gzip	Brotli
web-component-base	6.2.0	6.6 kB	2.9 kB	2.6 kB
@elenajs/core	1.0.1	9.2 kB	3.7 kB	3.4 kB
lit	3.3.3	15.3 kB	5.9 kB	5.3 kB
@microsoft/fast-element	3.0.1	44.8 kB	13.6 kB	12.2 kB
vanilla HTMLElement	-	0.6 kB	0.3 kB	0.2 kB

For scale: even after all of the v5.2–v6.2 work, the WCB counter is ~23% smaller than Elena, ~52% smaller than Lit, and ~79% smaller than FAST.

Feature comparison

What each library gives you beyond extending directly from HTMLElement, the boilerplate you no longer write by hand:

Capability	WCB 6.2	Lit 3.3	Elena 1.0	FAST 3.0
Declarative templates	✅ html tagged templates (htm) or plain strings	✅ lit-html tagged templates	✅ html tagged templates	✅ typed templates with binding expressions
Reactive props ⇄ attributes	✅ static props, overrideable converters	✅ static properties with converters	✅ static props, opt-in reflection	✅ @attr / observables
Update strategy	In-place patch (index-based, non-keyed)	Part-based: only touched bindings update, keyed repeat	Batched re-renders	Fine-grained observable bindings, keyed repeat
Preserves DOM state on re-render	✅	✅	✅	✅
Update batching / scheduling	⚠️ renders per prop write	✅ async batched, updateComplete	✅ batched, updateComplete	✅ queued/batched
Keyed list reconciliation	⚠️ positional	✅ repeat directive	⚠️ positional morph	✅ repeat with recycling controls
Light DOM by default	✅ (shadow DOM opt-in via static shadowRootInit)	❌ shadow DOM by default	✅ (shadow opt-in)	❌ shadow DOM by default
Scoped styles	⚠️ static styles needs shadow opt-in via static shadowRootInit	✅ shadow-scoped CSS (shadow DOM is the default)	✅ light DOM via generated @scope CSS files (CLI); static styles needs shadow opt-in	✅ shadow-scoped + design tokens (shadow default)
Server rendering	⚠️ no SSR package; typed prop state initializes from server-written attributes (any server, no server-side JS)	✅ @lit-labs/ssr (carries labs prerelease notice)	⚠️ @elenajs/ssr is experimental alpha	⚠️ fast-ssr deprecated; successor packages pre-1.0
Hydrates server DOM	❌ first client render replaces server markup	✅	❌ dynamic components replace server markup on first render	⚠️ defer-hydration exists, tied to deprecated/pre-1.0 stack
Works with zero build tooling	✅ import from CDN, no compiler	✅ (buildless possible, decorators need tooling)	✅	⚠️ practical with tooling
Editor/IDE tooling	✅ typed props + CEM analyzer plugin	✅ extensive (analyzer, TS decorators, IDE plugins)	✅ CEM-focused	✅ TS-first
Lifecycle hooks	onInit, afterViewInit, onChanges, onDestroy	full reactive update lifecycle	willUpdate, firstUpdated, updated	full lifecycle + behaviors
Backing / ecosystem	solo maintainer; one package, small surface	OpenJS Foundation (donated by Google 2025), large ecosystem	new (2026), solo-authored	Microsoft, powers Fluent UI

SSR and hydration

Each SSR cell quotes that package’s own stability designation. @lit-labs/ssr is the most mature despite the labs prerelease notice — it sits at major version 4 and ships actively. @microsoft/fast-ssr is deprecated in favor of @microsoft/fast-build and @microsoft/webui, both currently pre-1.0. WCB has no SSR package: state initializes from server-written attributes, but the server DOM is paint-only.

Why 11ty WebC isn’t here

WebC is a compile-time tool: it resolves components during an Eleventy build and ships plain HTML with no client runtime. Every row above is about what a library does in the browser at runtime, so a side-by-side comparison would be measuring two different things. If your components are static at build time, WebC solves a different problem.

For what these numbers and capabilities add up to (and when they don’t) see Why would anyone use WCB?.

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All libraries measured 2026-08-09 — WCB at v6.2.0 — with esbuild, Node zlib (gzip −9, brotli q11), at the pinned versions above. Methodology: identical counter component per library, bundled per library, compressed. Re-run them yourself — the counters and the measure.mjs script live in the demo workspace (demo/examples/library-comparison/). The benchmark is trivially reproducible with the versions pinned above.