Render Hyperapp to an HTML string with SSR and Node.js streaming support


2.1.03 years ago4 years agoMinified + gzip package size for @hyperapp/render in KB


Hyperapp Render

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A Hyperapp higher-order app that allows you to render views to an HTML string.

  • User experience — Generate HTML on the server and send the markup down on the initial request for faster page loads. Built-in mounting feature in Hyperapp is allowing you to have a very performant first-load experience.
  • Accessibility — Allow search engines to crawl your pages for SEO purposes.
  • TestabilityCheck HTML validity and use snapshot testing to improve quality of your software.

Getting Started

Our first example is an interactive app from which you can generate an HTML markup. Go ahead and try it online.

import { h, app } from 'hyperapp'
import { withRender } from '@hyperapp/render'

const state = {
  text: 'Hello'

const actions = {
  setText: text => ({ text })

const view = (state, actions) => (
    <h1>{state.text.trim() === '' ? '👋' : state.text}</h1>
    <input value={state.text} oninput={e => actions.setText(e.target.value)} />

const main = withRender(app)(state, actions, view)

main.toString()       // => <main><h1>Hello</h1><input value="Hello"/></main>
main.setText('World') // <= any sync or async action call
main.toString()       // => <main><h1>World</h1><input value="World"/></main>

Looking for a boilerplate? Try Hyperapp Starter with pre-configured server-side rendering and many more.


Using npm:

npm install @hyperapp/render --save

Or using a CDN like unpkg.com or jsDelivr with the following script tag:

<script src="https://unpkg.com/@hyperapp/render/hyperapp-render.min.js"></script>

You can find the library in window.hyperappRender.

We support all ES5-compliant browsers, including Internet Explorer 9 and above, but depending on your target browsers you may need to include polyfills for Set, Map and Object.assign before any other code.


The library provides a few functions which you can use depending on your needs or personal preferences.

import { withRender, renderToString, renderToStream } from '@hyperapp/render'

const main = withRender(app)(state, actions, view, container)

main.toString()                      // => <string>
renderToString(<Component />)        // => <string>
renderToString(view, state, actions) // => <string>

main.toStream()                      // => <stream.Readable> => <string>
renderToStream(<Component />)        // => <stream.Readable> => <string>
renderToStream(view, state, actions) // => <stream.Readable> => <string>

Note: functions toStream and renderToStream are available in Node.js environment only (v6 or newer).


The library exposes three functions. The first of these is withRender high-order function, which adds the toString action to be able to render your application to an HTML string at any given time. This can be useful for server-side rendering or creating HTML snippets based on current application state.

import { h, app } from 'hyperapp'
import { withRender } from '@hyperapp/render'

const state = { name: 'World' }
const actions = { setName: name => ({ name }) }
const view = (state, actions) => <h1>Hello {state.name}</h1>

const main = withRender(app)(state, actions, view)

main.toString()          // => <h1>Hello World</h1>
main.setName('Hyperapp') // <= any sync or async action call
main.toString()          // => <h1>Hello Hyperapp</h1>

The second renderToString function generates HTML markup from any of your views without app initialization. That could be useful to generate HTML markup from static views.

import { renderToString } from '@hyperapp/render'

const Component = ({ name }) => <h1>Hello {name}</h1>

renderToString(<Component name="World" />)
// => <h1>Hello World</h1>

The last renderToStream function and toStream equivalent return a Readable stream that outputs an HTML string. The HTML output by this stream is exactly equal to what toString or renderToString would return. They are designed for more performant server-side rendering and here are examples how they could be used with Express or Koa:

app.get('/', (req, res) => {
  res.write('<!doctype html><html><head>')
  res.write('</head><body><div id="app">')
  const main = withRender(app)(state, actions, view)
  const stream = main.toStream()
  stream.pipe(res, { end: false })
  stream.on('end', () => {
app.get('/', (req, res) => {
  res.write('<!doctype html>')
  const stream = renderToStream(
        <div id="app">{view(state, actions)}</div>


The library automatically escapes text content and attribute values of virtual DOM nodes to protect your application against XSS attacks.

However, it is not safe to allow "user input" for node names or attribute keys because the library does not reject injection attack on markup due to performance reasons. See:

const Node = 'div onclick="alert()"'
renderToString(<Node title="XSS">Hi</Node>)
// => <div onclick="alert()" title="XSS">Hi</div>

const attributes = { 'onclick="alert()" title': 'XSS' }
renderToString(<div {...attributes}>Hi</div>)
// => <div onclick="alert()" title="XSS">Hi</div>

const userInput = '<script>alert()</script>'
renderToString(<div title="XSS" innerHTML={userInput}>Hi</div>)
// => <div title="XSS"><script>alert()</script></div>


Hyperapp Render is MIT licensed. See LICENSE.

If you find any bugs or have a feature request, please open an issue on github!

The npm package download data comes from npm's download counts api and package details come from npms.io.