Astro and WebJs share a headline idea: send as little JavaScript as possible and hydrate only the interactive parts. Astro popularized the islands architecture, and WebJs arrives at a similar place from a different direction. Of the frameworks people compare WebJs to, Astro is arguably the closest in spirit. The differences are about what happens at build time versus request time, and how much of a full-stack backend each one is.
What the two agree on
- Ship less JavaScript. Both default to HTML-first output and treat client JS as opt-in, not the baseline.
- Islands. Astro hydrates interactive islands with
client:*directives; WebJs hydrates interactive web components per element. Same core idea, static shell plus interactive leaves. - Standards-friendly. Both are comfortable with plain HTML, and both let you use web components directly.
If Astro's "mostly static, sprinkle interactivity" model appeals to you, WebJs's model will feel related.
Difference one: build-time vs no build at all
Astro has a build step. It compiles .astro components and your islands into optimized output, and it excels at static and content-heavy sites, with a build to run for each deploy. WebJs has no build step. The .ts files you write are served directly with types stripped in place. There is no compile, and there is no static-generation build either; pages are rendered per request (with an opt-in HTML response cache for pages identical to every visitor).
So Astro is at its best when the content is known at build time and can be generated ahead. WebJs is at its best when content is dynamic and request-time, and it skips the build entirely.
Difference two: islands model
Astro's islands are components from a UI framework of your choice (React, Vue, Svelte, or web components) that you hydrate with explicit client:load, client:visible, and similar directives. You choose the framework and mark the hydration strategy.
WebJs's islands are always native web components, and the hydration is automatic. A component with an interactive signal hydrates; a display-only component with no signal renders identical HTML with or without its script, so WebJs strips its module from the download automatically. You do not annotate hydration; the framework derives it. The trade is less explicit control in exchange for not having to think about it, and a single component model rather than any-framework-you-like.
Difference three: how much backend you get
This is the largest difference. Astro is primarily a frontend and content framework. It has server endpoints and server-side rendering, and it added Server Actions, but the center of gravity is content: collections, markdown, static generation. You typically bring your own data and backend patterns.
WebJs is a full-stack framework first. Server actions are the core mechanism, with a .server.ts file becoming a typed RPC stub across the network boundary. It ships built-in auth, sessions, cookies, caching, and rate limiting over one pluggable store, plus Drizzle and Tailwind wired out of the box, plus a client router that preserves layout DOM across navigations. The backend is the point, not an addition.
Where Astro is the better pick
- You are building a content site, a blog, docs, or marketing pages where most content is known at build time and can be statically generated. Astro is superb at this and it is what it was built for.
- You want to mix components from React, Vue, and Svelte in one project, or bring an existing component from one of those frameworks.
- You want Astro's large content ecosystem: content collections, integrations, and a mature community.
- You want to deploy pure static output to any CDN with no server at all.
Where WebJs is the better pick
- You are building a dynamic application with real reads and writes, not a mostly-static content site, and you want the backend to be first-class.
- You want no build step for either dev or deploy, and request-time rendering rather than a static-generation step.
- You want automatic islands with native web components and automatic zero-JS elision, without annotating hydration.
- You want auth, sessions, caching, a data layer, and a typed server-action boundary built in rather than assembled.
Astro and WebJs both refuse to ship JavaScript you do not need. Astro reaches that as a build-time content framework you add islands to; WebJs reaches it as a no-build full-stack framework where the interactive web component is the unit and the server is built in.
FAQ
Do WebJs and Astro both use islands?
Yes, both send mostly static HTML and hydrate only the interactive parts. The difference is how. Astro uses client:* directives you annotate at build time; WebJs treats every interactive web component as an island automatically and elides display-only components to zero JavaScript with no annotation.
Does WebJs need a build step like Astro?
No. Astro compiles your site with a build step. WebJs serves native ES modules directly and strips TypeScript at load, so there is nothing to build. Both aim for minimal client JavaScript, but WebJs reaches it without a compile phase.
Should I pick Astro or WebJs for a content site?
Astro is excellent for content-heavy, largely static sites and has a mature content and integrations ecosystem. Pick WebJs when the app needs a built-in server story (auth, sessions, a typed server-action data boundary) and you want interactivity to be native web components with no build step.