Server Rendering

Zeus can compile the same TSX source to server-side string rendering code. The Vite plugin selects this target automatically while Vite is loading an SSR module.

Render HTML

Import the server API from the dedicated entry so a Node process does not load the DOM runtime:

import { For, Show, renderToString } from '@zeus-js/zeus/server'

function App(props: { signedIn: boolean; names: string[] }) {
  return (
    <main class="app">
      <Show when={props.signedIn} fallback={<p>Sign in</p>}>
        <ul>
          <For each={props.names}>{name => <li>{name}</li>}</For>
        </ul>
      </Show>
    </main>
  )
}

const html = renderToString(() => (
  <App signedIn={true} names={['Ada', 'Lin']} />
))

renderToString is synchronous. It executes the component tree once inside a dedicated reactive scope, serializes the result, and disposes the scope before returning. A Promise or custom thenable at any depth, including component results, text, attributes, class, style, or property values, throws renderToString() does not support async render values. Nothing in this API is awaited or silently omitted.

Vite Configuration

The normal plugin setup covers both browser and SSR transforms:

import { defineConfig } from 'vite'
import zeus from '@zeus-js/vite-plugin'

export default defineConfig({
  plugins: [zeus()],
})

Browser transforms import @zeus-js/runtime-dom. SSR transforms import @zeus-js/runtime-ssr. A custom SSR runtime can be selected independently:

zeus({ ssrModuleName: 'virtual:my-zeus-ssr-runtime' })

When using the Babel compiler directly, set generate: 'ssr' and point moduleName at the SSR runtime.

Serialization

Dynamic text and attribute values are HTML escaped. Nullish and boolean values produce no text; false and nullish attributes are omitted; true attributes are serialized without a value. Event handlers and refs are client-only and are not included in server HTML.

script and style children follow HTML raw-text rules. Ordinary < and & characters remain unchanged. A matching closing tag is rewritten safely after all children have been joined, including closing tags split across fragments or control-flow branches, so dynamic content cannot terminate the raw-text element early. Script serialization also rewrites <script when an earlier <!-- has put the HTML tokenizer into its escaped state, preventing the tokenizer from swallowing the following page in its double-escaped state.

Raw-text elements accept direct text expressions, Fragment, Show, and For. Nested native elements or components fail compilation with ZEUS_UNSUPPORTED_SSR_RAW_TEXT_CHILD; dynamic values that are already serialized SSR fragments fail at runtime because their original text context cannot be recovered.

SSR accepts prop:* only when the property has a deterministic HTML representation for that element. The supported bindings are:

• value on button, input, option, and textarea;
• checked on input and selected on option;
• multiple on input and select;
• disabled on button, fieldset, input, optgroup, option, select, and textarea;
• readOnly on input and textarea;
• htmlFor on label, plus tabIndex on any element.

Supported properties serialize only string, number, and boolean values; other value types are omitted. A serialized property binding replaces the equivalent static attribute. textarea value is the exception: it becomes escaped text content and replaces any JSX children. Other property/tag combinations, such as textContent, div.checked, or select.value, fail compilation with the structured ZEUS_UNSUPPORTED_SSR_PROPERTY diagnostic because they have no equivalent static HTML representation.

The initial SSR release does not hydrate the generated HTML. Mounting the same application in a browser creates a fresh DOM tree. Streaming, asynchronous SSR, and Web Components SSR are also outside the current contract.