rendu

🏎️ JavaScript Hypertext Preprocessor.

Rendu is a lightweight toolkit for mixing HTML and JavaScript with a focus on simplicity, standards and progressive rendering.

[!WARNING] This is an experimental PoC.

[!NOTE] See playground (online playground) for demos and syntax section for usage.

CLI

Using the rendu CLI, you can start a local web server to serve static files and render .html files as templates (powered by srvx).

npx rendu

Programmatic API

compileTemplate(template, opts)

Compile a template string into a render function.

Example:

import { compileTemplate } from "rendu";

const template = `
  <h1>{{ title }}</h1>
  <ul>
  <? for (const item of items) { ?>
    <li>{{ item }}</li>
  <? } ?>
  </ul>
`;

const render = compileTemplate(template, { stream: false });

const html = await render({ title: "My List", items: ["Item 1", "Item 2", "Item 3"] });
console.log(html);
// Output:
// <h1>My List</h1>
// <ul>
//   <li>Item 1</li>
//   <li>Item 2</li>
//   <li>Item 3</li>
// </ul>

compileTemplateToString(template, opts, asyncWrapper?)

Compile a template string into a render function code string.

Note: This function is for advanced use cases where you need the generated code as a string.

createRenderContext(options)

hasTemplateSyntax(template)

Check if a template string contains template syntax.

RENDER_CONTEXT_KEYS

• Type: array
• Default: ["htmlspecialchars","setCookie","redirect","$REQUEST","$METHOD","$URL","$HEADERS","$COOKIES","$RESPONSE"]

renderToResponse(htmlTemplate, opts)

Renders an HTML template to a Response object.

Example:

import { compileTemplate, renderToResponse } from "rendu";

const render = compileTemplate(template, { stream: true });

const response = await renderToResponse(render, { request });

Syntax

Rendu uses PHP-style tags to embed JavaScript within HTML templates:

Server Scripts

Use <script server> to execute JavaScript on the server where it appears:

<script server>
  globalThis.visitedPagesCount ??= 0;
  globalThis.visitedPagesCount++;
</script>

Output Expressions

Use {{ expression }} for HTML-escaped output, or {{{ expression }}} or <?= expression ?> for unescaped (raw) output:

<h1><?= title ?></h1>
<div>Page visited: {{ visitedPagesCount }}</div>

Control Structures

Use <? ... ?> for JavaScript control flow:

<? if (items.length === 0) { ?>
<p>No items found.</p>
<? } ?> <? for (const item of items) { ?>
<li>{{ item.name }}</li>
<? } ?>

Streaming Content

Use the echo() function for streaming content. Accepts: strings, functions, Promises, Response objects, or ReadableStreams:

Examples:

<!-- Simple string output -->
<script server>
  echo("Welcome to our site!");
</script>

<!-- Async content from API (non-blocking)-->
<script server>
  echo("Hello");
  echo(async () => fetch("https://api.example.com/data"));
  echo(() => "World");
</script>

Global Variables

Access request context and global state:

• $REQUEST: The incoming Request object
• $METHOD: HTTP method (GET, POST, etc.)
• $URL: Request URL object
• $HEADERS: Request headers
• $RESPONSE: Response configuration object
• $COOKIES: Read-only object containing request cookies

Cookie Management

Use setCookie() function to set cookies in the response:

<script server>
  setCookie("user", "RenduUser");
  setCookie("session", "abc123", { maxAge: 3600, httpOnly: true });
</script>

Access cookies from the request using $COOKIES:

<div>Welcome, <?= $COOKIES["user"] || "Guest" ?>!</div>

Response Control

Use redirect() function to redirect the user:

<script server>
  if (!$COOKIES["auth"]) {
    redirect("/login");
  }
</script>

HTML Escaping

The htmlspecialchars() function is available for escaping HTML content:

[!TIP] When using curly {{ }} syntax, htmlspecialchars will be automatically applied.

<div><?= htmlspecialchars(userInput) ?></div>

Development

• Clone this repository
• Install the latest LTS version of Node.js
• Enable Corepack using corepack enable
• Install dependencies using pnpm install
• Run interactive tests using pnpm dev

Prior Art

• jaubourg/jhp
• atinux/pjs
• mde/ejs

License

Published under the MIT license.