mono-jsx

mono-jsx is a JSX runtime that renders <html> element to Response object in JavaScript runtimes like Node.js, Deno, Bun, Cloudflare Workers, etc.

🚀 No build step needed
🦋 Lightweight (8KB gzipped), zero dependencies
🚦 Signals as reactive primitives
🗂️ Complete Web API TypeScript definitions
⏳ Streaming rendering
🥷 htmx integration
🌎 Universal, works in Node.js, Deno, Bun, Cloudflare Workers, etc.

Installation

mono-jsx supports all modern JavaScript runtimes including Node.js, Deno, Bun, and Cloudflare Workers. You can install it via npm, deno, or bun:

# Node.js, Cloudflare Workers, or other node-compatible runtimes
npm i mono-jsx

# Deno
deno add npm:mono-jsx

# Bun
bun add mono-jsx

Setup JSX Runtime

To use mono-jsx as your JSX runtime, add the following configuration to your tsconfig.json (or deno.json for Deno):

{
  "compilerOptions": {
    "jsx": "react-jsx",
    "jsxImportSource": "mono-jsx"
  }
}

Alternatively, you can use a pragma directive in your JSX file:

/** @jsxImportSource mono-jsx */

You can also run mono-jsx setup to automatically add the configuration to your project:

# Node.js, Cloudflare Workers, or other node-compatible runtimes
npx mono-jsx setup

# Deno
deno run -A npm:mono-jsx setup

# Bun
bunx mono-jsx setup

Usage

mono-jsx allows you to return an <html> JSX element as a Response object in the fetch handler:

// app.tsx

export default {
  fetch: (req) => (
    <html>
      <h1>Welcome to mono-jsx!</h1>
    </html>
  )
}

For Deno/Bun users, you can run the app.tsx directly:

deno serve app.tsx
bun run app.tsx

If you're building a web app with Cloudflare Workers, use wrangler dev to start local development:

npx wrangler dev app.tsx

Node.js doesn't support JSX syntax or declarative fetch servers, so we recommend using mono-jsx with srvx:

// app.tsx

import { serve } from "srvx";

serve({
  port: 3000,
  fetch: (req) => (
    <html>
      <h1>Welcome to mono-jsx!</h1>
    </html>
  ),
});

You'll need tsx to start the app without a build step:

npx tsx app.tsx

Note

Only root <html> element will be rendered as a Response object. You cannot return a <div> or any other element directly from the fetch handler. This is a limitation of the mono-jsx runtime.

Using JSX

mono-jsx uses JSX to describe the user interface, similar to React but with key differences.

Using Standard HTML Property Names

mono-jsx adopts standard HTML property names, avoiding React's custom naming conventions:

className → class
htmlFor → for
onChange → onInput

Composition with `class`

mono-jsx allows you to compose the class property using arrays of strings, objects, or expressions:

<div
  class={[
    "container box",
    isActive && "active",
    { hover: isHover },
  ]}
/>;

Using Pseudo Classes and Media Queries in `style`

mono-jsx supports pseudo classes, pseudo elements, media queries, and CSS nesting in the style property:

<a
  style={{
    color: "black",
    "::after": { content: "↩️" },
    ":hover": { textDecoration: "underline" },
    "@media (prefers-color-scheme: dark)": { color: "white" },
    "& .icon": { width: "1em", height: "1em", marginRight: "0.5em" },
  }}
>
  <img class="icon" src="link.png" />
  Link
</a>;

Using `<slot>` Element

mono-jsx uses <slot> elements to render slotted content (equivalent to React's children property). You can also add the name attribute to define named slots:

function Container() {
  return (
    <div class="container">
      {/* Default slot */}
      <slot />
      {/* Named slot */}
      <slot name="desc" />
    </div>
  )
}

function App() {
  return (
    <Container>
      {/* This goes to the named slot */}
      <p slot="desc">This is a description.</p>
      {/* This goes to the default slot */}
      <h1>Hello world!</h1>
    </Container>
  )
}

Using `html` Tag Function

mono-jsx provides an html tag function to render raw HTML in JSX instead of React's dangerouslySetInnerHTML:

function App() {
  return <div>{html`<h1>Hello world!</h1>`}</div>;
}

The html tag function is globally available without importing. You can also use css and js tag functions for CSS and JavaScript:

function App() {
  return (
    <head>
      <style>{css`h1 { font-size: 3rem; }`}</style>
      <script>{js`console.log("Hello world!")`}</script>
    </head>
  )
}

Warning

The html tag function is unsafe and can cause XSS vulnerabilities.

Event Handlers

mono-jsx lets you write event handlers directly in JSX, similar to React:

function Button() {
  return (
    <button onClick={(evt) => alert("BOOM!")}>
      Click Me
    </button>
  )
}

Note

Event handlers are never called on the server-side. They're serialized to strings and sent to the client. This means you should NOT use server-side variables or functions in event handlers.

import { doSomething } from "some-library";

function Button(this: FC<{ count: 0 }>, props: { role: string }) {
  const message = "BOOM!";        // server-side variable
  this.count = 0;                 // initialize a signal
  console.log(message);           // only prints on server-side
  return (
    <button
      role={props.role}
      onClick={(evt) => {
        alert(message);           // ❌ `message` is a server-side variable
        console.log(props.role);  // ❌ `props` is a server-side variable
        doSomething();            // ❌ `doSomething` is imported on the server-side
        Deno.exit(0);             // ❌ `Deno` is unavailable in the browser
        document.title = "BOOM!"; // ✅ `document` is a browser API
        console.log(evt.target);  // ✅ `evt` is the event object
        this.count++;             // ✅ update the `count` signal
      }}
    >
      <slot />
    </button>
  )
}

Using `<form>` Element

mono-jsx supports <form> elements with the action attribute. The action attribute can be a string URL or a function that accepts a FormData object. The function will be called on form submission, and the FormData object will contain the form data.

function App() {
  return (
    <form action={(data: FormData) => console.log(data.get("name"))}>
      <input type="text" name="name" />
      <button type="submit">Submit</button>
    </form>
  )
}

Async Components

mono-jsx supports async components that return a Promise or an async function. With streaming rendering, async components are rendered asynchronously, allowing you to fetch data or perform other async operations before rendering the component.

async function Loader(props: { url: string }) {
  const data = await fetch(url).then((res) => res.json());
  return <JsonViewer data={data} />;
}

export default {
  fetch: (req) => (
    <html>
      <Loader url="https://api.example.com/data" placeholder={<p>Loading...</p>} />
    </html>
  )
}

You can also use async generators to yield multiple elements over time. This is useful for streaming rendering of LLM tokens:

async function* Chat(props: { prompt: string }) {
  const stream = await openai.chat.completions.create({
    model: "gpt-4",
    messages: [{ role: "user", content: prompt }],
    stream: true,
  });

  for await (const event of stream) {
    const text = event.choices[0]?.delta.content;
    if (text) {
      yield <span>{text}</span>;
    }
  }
}

export default {
  fetch: (req) => (
    <html>
      <Chat prompt="Tell me a story" placeholder={<span style="color:grey">●</span>} />
    </html>
  )
}

Using Signals

mono-jsx uses signals for updating the view when a signal changes. Signals are similar to React's state, but they are more lightweight and efficient. You can use signals to manage state in your components.

Using Component Signals

You can use the this keyword in your components to manage signals. The signals is bound to the component instance and can be updated directly, and will automatically re-render the view when a signal changes:

function Counter(
  this: FC<{ count: number }>,
  props: { initialCount?: number },
) {
  // Initialize a singal
  this.count = props.initialCount ?? 0;

  return (
    <div>
      {/* render singal */}
      <span>{this.count}</span>

      {/* Update singal to trigger re-render */}
      <button onClick={() => this.count--}>-</button>
      <button onClick={() => this.count++}>+</button>
    </div>
  )
}

Using App Signals

You can define app signals by adding app prop to the root <html> element. The app signals is available in all components via this.app.<SignalName>. Changes to the app signals will trigger re-renders in all components that use it:

interface AppSignals {
  themeColor: string;
}

function Header(this: FC<{}, AppSignals>) {
  return (
    <header>
      <h1 style={this.computed(() => ({ color: this.app.themeColor }))}>Welcome to mono-jsx!</h1>
    </header>
  )
}

function Footer(this: FC<{}, AppSignals>) {
  return (
    <footer>
      <p style={this.computed(() => ({ color: this.app.themeColor }))}>(c) 2025 mono-jsx.</p>
    </footer>
  )
}

function Main(this: FC<{}, AppSignals>) {
  return (
    <main>
      <p>
        <label>Theme Color: </label>
        <input type="color" onInput={({ target }) => this.app.themeColor = target.value}/>
      </p>
    </main>
  )
}

export default {
  fetch: (req) => (
    <html app={{ themeColor: "#232323" }}>
      <Header />
      <Main />
      <Footer />
    </html>
  )
}

Using Computed Signals

You can use this.computed to create a derived signal based on other signals:

function App(this: FC<{ input: string }>) {
  this.input = "Welcome to mono-jsx";
  return (
    <div>
      <h1>{this.computed(() => this.input + "!")}</h1>

      <form action={(fd) => this.input = fd.get("input") as string}>
        <input type="text" name="input" value={"" + this.input} />
        <button type="submit">Submit</button>
      </form>
    </div>
  )
}

Using Effects

You can use this.effect to create side effects based on signals. The effect will run whenever the signal changes:

function App(this: FC<{ count: number }>) {
  this.count = 0;

  this.effect(() => {
    console.log("Count changed:", this.count);
  });

  return (
    <div>
      <span>{this.count}</span>
      <button onClick={() => this.count++}>+</button>
    </div>
  )
}

The callback function of this.effect can return a cleanup function that gets run once the component element has been removed via <toggle> or <switch> condition rendering:

function Counter(this: FC<{ count: number }>) {
  this.count = 0;

  this.effect(() => {
    const interval = setInterval(() => {
      this.count++;
    }, 1000);

    return () => clearInterval(interval);
  });

  return (
    <div>
      <span>{this.count}</span>
    </div>
  )
}

function App(this: FC<{ show: boolean }>) {
  this.show = true
  return (
    <div>
      <toggle show={this.show}>
        <Foo />
      </toggle>
      <button onClick={e => this.show = !this.show }>{this.computed(() => this.show ? 'Hide': 'Show')}</button>
    </div>
  )
}

Using `<toggle>` Element with Signals

The <toggle> element conditionally renders content based on the show prop:

function App(this: FC<{ show: boolean }>) {
  this.show = false;

  function toggle() {
    this.show = !this.show;
  }

  return (
    <div>
      <toggle show={this.show}>
        <h1>Welcome to mono-jsx!</h1>
      </toggle>

      <button onClick={toggle}>
        {this.computed(() => this.show ? "Hide" : "Show")}
      </button>
    </div>
  )
}

Using `<switch>` Element with Signals

The <switch> element renders different content based on the value of a signal. Elements with matching slot attributes are displayed when their value matches, otherwise default slots are shown:

function App(this: FC<{ lang: "en" | "zh" | "🙂" }>) {
  this.lang = "en";

  return (
    <div>
      <switch value={this.lang}>
        <h1 slot="en">Hello, world!</h1>
        <h1 slot="zh">你好，世界！</h1>
        <h1>✋🌎❗️</h1>
      </switch>
      <p>
        <button onClick={() => this.lang = "en"}>English</button>
        <button onClick={() => this.lang = "zh"}>中文</button>
        <button onClick={() => this.lang = "🙂"}>🙂</button>
      </p>
    </div>
  )
}

Limitation of Signals

1. Arrow function are non-stateful components.

// ❌ Won't work - use `this` in a non-stateful component
const App = () => {
  this.count = 0;
  return (
    <div>
      <span>{this.count}</span>
      <button onClick={() => this.count++}>+</button>
    </div>
  )
};

// ✅ Works correctly
function App(this: FC) {
  this.count = 0;
  return (
    <div>
      <span>{this.count}</span>
      <button onClick={() => this.count++}>+</button>
    </div>
  )
}

2. Signals cannot be computed outside of the this.computed method.

// ❌ Won't work - updates of a signal won't refresh the view
function App(this: FC<{ message: string }>) {
  this.message = "Welcome to mono-jsx";
  return (
    <div>
      <h1 title={this.message + "!"}>{this.message + "!"}</h1>
      <button onClick={() => this.message = "Clicked"}>
        Click Me
      </button>
    </div>
  )
}

// ✅ Works correctly
function App(this: FC) {
  this.message = "Welcome to mono-jsx";
  return (
    <div>
      <h1 title={this.computed(() => this.message + "!")}>{this.computed(() => this.message + "!")}</h1>
      <button onClick={() => this.message = "Clicked"}>
        Click Me
      </button>
    </div>
  )
}

3. The callback function of this.computed must be a pure function. That means it should not create side effects or access any non-stateful variables. For example, you cannot use Deno or document in the callback function:

// ❌ Won't work - throws `Deno is not defined` when the button is clicked
function App(this: FC<{ message: string }>) {
  this.message = "Welcome to mono-jsx";
  return (
    <div>
      <h1>{this.computed(() => this.message + "! (Deno " + Deno.version.deno + ")")}</h1>
      <button onClick={() => this.message = "Clicked"}>
        Click Me
      </button>
    </div>
  )
}

// ✅ Works correctly
function App(this: FC<{ message: string, denoVersion: string }>) {
  this.denoVersion = Deno.version.deno;
  this.message = "Welcome to mono-jsx";
  return (
    <div>
      <h1>{this.computed(() => this.message + "! (Deno " + this.denoVersion + ")")}</h1>
      <button onClick={() => this.message = "Clicked"}>
        Click Me
      </button>
    </div>
  )
}

Using `this` in Components

mono-jsx binds a scoped signals object to this of your component functions. This allows you to access signals, context, and request information directly in your components.

The this object has the following built-in properties:

app: The app signals defined on the root <html> element.
context: The context defined on the root <html> element.
request: The request object from the fetch handler.
refs: A map of refs defined in the component.
computed: A method to create a computed signal.
effect: A method to create side effects.

type FC<Signals = {}, AppSignals = {}, Context = {}> = {
  readonly app: AppSignals;
  readonly context: Context;
  readonly request: Request;
  readonly refs: Record<string, HTMLElement | null>;
  readonly computed: <T = unknown>(fn: () => T) => T;
  readonly effect: (fn: () => void | (() => void)) => void;
} & Omit<Signals, "app" | "context" | "request" | "computed" | "effect">;

Using Signals

See the Using Signals section for more details on how to use signals in your components.

Using Refs

You can use this.refs to access refs in your components. Define refs in your component using the ref attribute:

function App(this: FC) {
  this.effect(() => {
    this.refs.input?.addEventListener("input", (evt) => {
      console.log("Input changed:", evt.target.value);
    });
  });

  return (
    <div>
      <input ref={this.refs.input} type="text" />
      <button onClick={() => this.refs.input?.focus()}>Focus</button>
    </div>
  )
}

Using Context

You can use the context property in this to access context values in your components. The context is defined on the root <html> element:

function Dash(this: FC<{}, {}, { auth: { uuid: string; name: string } }>) {
  const { auth } = this.context;
  return (
    <div>
      <h1>Welcome back, {auth.name}!</h1>
      <p>Your UUID is {auth.uuid}</p>
    </div>
  )
}

export default {
  fetch: async (req) => {
    const auth = await doAuth(req);
    return (
      <html context={{ auth }} request={req}>
        {!auth && <p>Please Login</p>}
        {auth && <Dash />}
      </html>
    )
  }
}

Accessing Request Info

You can access request information in components via the request property in this which is set on the root <html> element:

function RequestInfo(this: FC) {
  const { request } = this;
  return (
    <div>
      <h1>Request Info</h1>
      <p>{request.method}</p>
      <p>{request.url}</p>
      <p>{request.headers.get("user-agent")}</p>
    </div>
  )
}

export default {
  fetch: (req) => (
    <html request={req}>
      <RequestInfo />
    </html>
  )
}

Streaming Rendering

mono-jsx renders your <html> as a readable stream, allowing async components to render asynchronously. You can use placeholder to display a loading state while waiting for async components to render:

async function Sleep({ ms }) {
  await new Promise((resolve) => setTimeout(resolve, ms));
  return <slot />;
}

export default {
  fetch: (req) => (
    <html>
      <Sleep ms={1000} placeholder={<p>Loading...</p>}>
        <p>After 1 second</p>
      </Sleep>
    </html>
  )
}

You can set the rendering attribute to "eager" to force synchronous rendering (the placeholder will be ignored):

export default {
  fetch: (req) => (
    <html>
      <Sleep ms={1000} rendering="eager">
        <p>After 1 second</p>
      </Sleep>
    </html>
  )
}

You can add the catch attribute to handle errors in the async component. The catch attribute should be a function that returns a JSX element:

async function Hello() {
  throw new Error("Something went wrong!");
  return <p>Hello world!</p>;
}

export default {
  fetch: (req) => (
    <html>
      <Hello catch={err => <p>{err.message}</p>} />
    </html>
  )
}

Customizing html Response

You can add status or headers attributes to the root <html> element to customize the http response:

export default {
  fetch: (req) => (
    <html
      status={404}
      headers={{
        cacheControl: "public, max-age=0, must-revalidate",
        setCookie: "name=value",
        "x-foo": "bar",
      }}
    >
      <h1>Page Not Found</h1>
    </html>
  )
}

Using htmx

mono-jsx integrates with htmx and typed-htmx. To use htmx, add the htmx attribute to the root <html> element:

export default {
  fetch: (req) => {
    const url = new URL(req.url);

    if (url.pathname === "/clicked") {
      return (
        <html>
          <span>Clicked!</span>
        </html>
      );
    }

    return (
      <html htmx>
        <button hx-get="/clicked" hx-swap="outerHTML">
          Click Me
        </button>
      </html>
    )
  }
}

Adding htmx Extensions

You can add htmx extensions by adding the htmx-ext-* attribute to the root <html> element:

export default {
  fetch: (req) => (
    <html htmx htmx-ext-response-targets htmx-ext-ws>
      <button hx-get="/clicked" hx-swap="outerHTML">
        Click Me
      </button>
    </html>
  )
}

Specifying htmx Version

You can specify the htmx version by setting the htmx attribute to a specific version:

export default {
  fetch: (req) => (
    <html htmx="2.0.4" htmx-ext-response-targets="2.0.2" htmx-ext-ws="2.0.2">
      <button hx-get="/clicked" hx-swap="outerHTML">
        Click Me
      </button>
    </html>
  )
}

Installing htmx Manually

By default, mono-jsx installs htmx from esm.sh CDN when you set the htmx attribute. You can also install htmx manually with your own CDN or local copy:

export default {
  fetch: (req) => (
    <html>
      <head>
        <script src="https://unpkg.com/htmx.org@2.0.4" integrity="sha384-HGfztofotfshcF7+8n44JQL2oJmowVChPTg48S+jvZoztPfvwD79OC/LTtG6dMp+" crossorigin="anonymous"></script>
        <script src="https://unpkg.com/htmx-ext-ws@2.0.2" integrity="sha384-vuKxTKv5TX/b3lLzDKP2U363sOAoRo5wSvzzc3LJsbaQRSBSS+3rKKHcOx5J8doU" crossorigin="anonymous"></script>
      </head>
      <body>
        <button hx-get="/clicked" hx-swap="outerHTML">
          Click Me
        </button>
      </body>
    </html>
  )
}

License

MIT

Name		Name	Last commit message	Last commit date
Latest commit History 173 Commits
.github		.github
runtime		runtime
test		test
types		types
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
build.ts		build.ts
deno.json		deno.json
dprint.json		dprint.json
index.ts		index.ts
jsx-runtime.ts		jsx-runtime.ts
package.json		package.json
render.ts		render.ts
setup.ts		setup.ts
symbols.ts		symbols.ts

License

ije/mono-jsx

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mono-jsx

Installation

Setup JSX Runtime

Usage

Using JSX

Using Standard HTML Property Names

Composition with class

Using Pseudo Classes and Media Queries in style

Using <slot> Element

Using html Tag Function

Event Handlers

Using <form> Element

Async Components

Using Signals

Using Component Signals

Using App Signals

Using Computed Signals

Using Effects

Using <toggle> Element with Signals

Using <switch> Element with Signals

Limitation of Signals

Using this in Components

Using Signals

Using Refs

Using Context

Accessing Request Info

Streaming Rendering

Customizing html Response

Using htmx

Adding htmx Extensions

Specifying htmx Version

Installing htmx Manually

License

About

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Languages

Composition with `class`

Using Pseudo Classes and Media Queries in `style`

Using `<slot>` Element

Using `html` Tag Function

Using `<form>` Element

Using `<toggle>` Element with Signals

Using `<switch>` Element with Signals

Using `this` in Components

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