Isomorphic hyperHTML
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hyperHTML lightness, ease, and performance, for the server.

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Same API without DOM constrains

Similar to its browser side counterpart, viperHTML parses the template string once, decides what is an attribute, what is a callback, what is text and what is HTML, and any future call to the same render will only update parts of that string.

The result is a blazing fast template engine that makes templates and renders shareable between the client and the server.

Seamlessly Isomorphic

No matter if you use ESM or CommonJS, you can use hypermorphic to load same features on both client and server.

// ESM example (assuming bundlers/ESM loaders in place)
import {bind, wire} from 'hypermorphic';

// CommonJS example
const {bind, wire} = require('hypermorphic');

Automatically Sanitized HTML

Both attributes and text nodes are safely escaped on each call.

const viperHTML = require('viperhtml');

var output = render => render`
  <!-- attributes and callbacks are safe -->
    <!-- also text is always safe -->
    <!-- use Arrays to opt-in HTML -->

var a = {
  text: 'Click "Me"',
  html: '<strong>"HTML" Me</strong>',
  href: '',
  onclick: (e) => e.preventDefault()

// associate the link to an object of info
// or simply use viperHTML.wire();
var link = viperHTML.bind(a);


The resulting output will be the following one:

  <!-- attributes and callbacks are safe -->
    onclick="return ((e) =&gt; e.preventDefault()).call(this, event)"
    <!-- also text is always safe -->
    Click &quot;Me&quot;
    <!-- HTML goes in as it is -->
    <span><strong>"HTML" Me</strong></span>

Usage Example

const viperHTML = require('viperhtml');

function tick(render) {
  return render`
      <h1>Hello, world!</h1>
      <h2>It is ${new Date().toLocaleTimeString()}.</h2>

// for demo purpose only,
// stop showing tick result after 6 seconds
    render => console.log(tick(render).toString()),
    // On a browser, you'll need to bind
    // the content to a generic DOM node.
    // On the server, you can directly use a wire()
    // which will produce an updated result each time
    // it'll be used through a template literal

The Extra viperHTML Feature: Asynchronous Partial Output

Clients and servers inevitably have different needs, and the ability to serve chunks on demand, instead of a whole page at once, is once of these very important differences that wouldn't make much sense on the client side.

If your page content might arrive on demand and is asynchronous, viperHTML offers an utility to both obtain performance boots, and intercepts all chunks of layout, as soon as this is available.


Similar to a wire, viperHTML.async() returns a callback that must be invoked right before the template string, optionally passing a callback that will be invoked per each available chunk of text, as soon as this is resolved.

// the view
const pageLayout = (render, model) =>
render`<!doctype html>

// the viper async render
const asyncRender = viperHTML.async();

// dummy server for one view only
  .createServer((req, res) => {
    res.writeHead( 200, {
      'Content-Type': 'text/html'

      // res.write(chunk) while resolved
      asyncRender(chunk => res.write(chunk)),

      // basic model example with async content
        head: Promise.resolve({html: '<title>right away</title>'}),
        body: new Promise(res => setTimeout(
          res, 1000,
          // either:
          //  {html: '<div>later on</div>'}
          //  ['<div>later on</div>']
          //  wire()'<div>later on</div>'
          viperHTML.wire()`<div>later on</div>`
    .then(() => res.end())
    .catch(err => { console.error(err); res.end(); });

Handy Patterns

Following a list of handy patterns to solve common issues.

HTML in template literals doesn't get highlighted

True that, but if you follow a simple (render, model) convetion, you can just have templates as html files.

<!-- template/tick.html -->
  <h1>Hello, ${}!</h1>
  <h2>It is ${new Date().toLocaleTimeString()}.</h2>

At this point, you can generate as many views as you want through the following step

#!/usr/bin/env bash

mkdir -p view

for f in $(ls template); do
  echo 'module.exports = (render, model) => render`' > "view/${f:0:-4}js"
  cat template/$f >> "view/${f:0:-4}js"
  echo '`;' >> "view/${f:0:-4}js"

As result, the folder view will now contain a tick.js file as such:

module.exports = (render, model) => render`
<!-- template/tick.html -->
  <h1>Hello, ${}!</h1>
  <h2>It is ${new Date().toLocaleTimeString()}.</h2>

You can now use each view as modules.

const view = {
  tick: require('./view/tick')

// show the result in console
  {name: 'user'}