HTML rendering engine

Usage no npm install needed!

<script type="module">
  import repaint from '';



A HTML layout engine written in Javascript. Takes HTML as input, renders it and outputs an image.

Parses HTML, CSS, combines them and then calculates position and dimensions of all elements. It's essentially the same as your browser's rendering engine.


Three years ago @devongovett claimed that he had ported WebKit to Javascript. Obviously it was a hoax as it makes no sense to run a browser in a browser.

But then in August I happened to run into a post by Matt Brubeck who wanted to write a browser engine in Rust, and it got me thinking. So I started working on this project around that time, and I now think it's ready to be judged by others.

There are still a lot of functionalities missing, but it is able to render some basic HTML. Right now it only works in the browser, but might be made to run in a node environment with some modifications.


The repaint-chrome repository provides a simple interface for editing and rendering markdown and HTML using repaint. The markdown is rendered by first converting it to plain HTML.


Available on npm.

npm install repaint

The module exposes a rendering function which accepts an options object and a callback. The content, context and viewport.dimensions.width options are required, and should respectively provide the HTML content as a string, the canvas 2d context used for drawing and the initial viewport width.

Additionally the url is used to resolve any resources linked in the HTML (images and stylesheet links), also viewport.position specifies the initial viewport offset, e.g. a position of { x: 0, y: -10 } would correspond to scrolling the page down 10 pixels.

Require the module with browserify or a similar tool.

var repaint = require('repaint');

    url: '' + window.location,
    stylesheets: ['body { color: red; }'],
    content: '<html><body>Hello</body></html>',
    context: canvas.getContext('2d'),
    viewport: {
        position: { x: 0, y: 0 },
        dimensions: { width: 512, height: 1024 }
}, function(err, page) {
    if(err) throw err;

The resulting page object contains some rendering details, like the parsed HTML (page.document) and the layout tree (page.layout).

The provided content is first parsed using the htmlparser2 module, and all stylesheets, including style attributes, are parsed with css and matched to HTML nodes with css-select. Before drawing the HTML the layout tree is constructed. Each node in the tree has the absolute position and dimensions calculated, and the text content is laid out according to the specification (e.g. each text line is contained in a line box).

There is no default stylesheet included, so all css properties fallback to their default values. This also means that everything in the head tag will be visible unless explicitly hidden.

It's possible to use the stylesheets option to provide styles that will be included before all other stylesheets in the HTML.

The module tries to follow the CSS 2.1 specification.


At the moment only normal flow is implemented, and without support for lists and tables.

Follows a non-exhaustive list of missing functionallity.

  • Collapsing margins
  • Background images
  • Inline blocks
  • Support for more vertical align values
  • Text decoration and align
  • Lists and counter properties (counter-reset and counter-increment)
  • Tables
  • Pseudo elements, :before, :after and the content property
  • overflow property
  • float and clear property
  • position property
  • CSS media types (@media rule)
  • Rounded corners (CSS3 functionallity, but would be nice to have)