dom-to-image

What is dom-to-image?

The dom-to-image npm package allows you to convert DOM nodes into images. It supports various output formats such as PNG, JPEG, and SVG. This can be useful for creating screenshots, generating thumbnails, or exporting visual content from web applications.

What are dom-to-image's main functionalities?

Convert DOM to PNG

This feature allows you to convert a DOM node to a PNG image. The resulting image is appended to the body of the document.

domtoimage.toPng(document.getElementById('my-node')).then(function (dataUrl) {
  var img = new Image();
  img.src = dataUrl;
  document.body.appendChild(img);
}).catch(function (error) {
  console.error('oops, something went wrong!', error);
});

Convert DOM to JPEG

This feature allows you to convert a DOM node to a JPEG image with a specified quality. The resulting image is downloaded as a file.

domtoimage.toJpeg(document.getElementById('my-node'), { quality: 0.95 }).then(function (dataUrl) {
  var link = document.createElement('a');
  link.download = 'my-image-name.jpeg';
  link.href = dataUrl;
  link.click();
}).catch(function (error) {
  console.error('oops, something went wrong!', error);
});

Convert DOM to SVG

This feature allows you to convert a DOM node to an SVG image. The resulting image is appended to the body of the document.

domtoimage.toSvg(document.getElementById('my-node')).then(function (dataUrl) {
  var img = new Image();
  img.src = dataUrl;
  document.body.appendChild(img);
}).catch(function (error) {
  console.error('oops, something went wrong!', error);
});

Convert DOM to Blob

This feature allows you to convert a DOM node to a Blob object. The resulting Blob can be saved as a file using the FileSaver.js library.

domtoimage.toBlob(document.getElementById('my-node')).then(function (blob) {
  window.saveAs(blob, 'my-node.png');
}).catch(function (error) {
  console.error('oops, something went wrong!', error);
});

Other packages similar to dom-to-image

html-to-image

The html-to-image package provides similar functionality to dom-to-image, allowing you to convert HTML nodes to images. It supports PNG, JPEG, and SVG formats. Compared to dom-to-image, html-to-image offers better support for modern web standards and improved performance.

html2canvas

The html2canvas package allows you to take 'screenshots' of webpages or parts of webpages directly in the browser. It renders the DOM to a canvas element, which can then be converted to an image. html2canvas is more mature and widely used compared to dom-to-image, but it may not support all CSS properties and complex layouts as well as dom-to-image.

canvas2image

The canvas2image package is a utility for converting canvas elements to image files. While it does not directly convert DOM nodes to images, it can be used in conjunction with libraries like html2canvas to achieve similar results. It is more focused on handling canvas elements and provides additional options for image manipulation.

README

DOM to Image

What is it

dom-to-image is a library which can turn arbitrary DOM node into a vector (SVG) or raster (PNG or JPEG) image, written in JavaScript. It's based on domvas by Paul Bakaus and has been completely rewritten, with some bugs fixed and some new features (like web font and image support) added.

Installation

NPM

npm install dom-to-image

Then load

/* in ES 6 */
import domtoimage from 'dom-to-image';
/* in ES 5 */
var domtoimage = require('dom-to-image');

Bower

bower install dom-to-image

Include either src/dom-to-image.js or dist/dom-to-image.min.js in your page and it will make the domtoimage variable available in the global scope.

<script src="path/to/dom-to-image.min.js" />
<script>
  domtoimage.toPng(node)
  //...
</script>

Usage

All the top level functions accept DOM node and rendering options, and return promises, which are fulfilled with corresponding data URLs.
Get a PNG image base64-encoded data URL and display right away:

var node = document.getElementById('my-node');

domtoimage.toPng(node)
    .then(function (dataUrl) {
        var img = new Image();
        img.src = dataUrl;
        document.body.appendChild(img);
    })
    .catch(function (error) {
        console.error('oops, something went wrong!', error);
    });

Get a PNG image blob and download it (using FileSaver, for example):

domtoimage.toBlob(document.getElementById('my-node'))
    .then(function (blob) {
        window.saveAs(blob, 'my-node.png');
    });

Save and download a compressed JPEG image:

domtoimage.toJpeg(document.getElementById('my-node'), { quality: 0.95 })
    .then(function (dataUrl) {
        var link = document.createElement('a');
        link.download = 'my-image-name.jpeg';
        link.href = dataUrl;
        link.click();
    });

Get an SVG data URL, but filter out all the <i> elements:

function filter (node) {
    return (node.tagName !== 'i');
}

domtoimage.toSvg(document.getElementById('my-node'), {filter: filter})
    .then(function (dataUrl) {
        /* do something */
    });

Get the raw pixel data as a Uint8Array with every 4 array elements representing the RGBA data of a pixel:

var node = document.getElementById('my-node');

domtoimage.toPixelData(node)
    .then(function (pixels) {
        for (var y = 0; y < node.scrollHeight; ++y) {
          for (var x = 0; x < node.scrollWidth; ++x) {
            pixelAtXYOffset = (4 * y * node.scrollHeight) + (4 * x);
            /* pixelAtXY is a Uint8Array[4] containing RGBA values of the pixel at (x, y) in the range 0..255 */
            pixelAtXY = pixels.slice(pixelAtXYOffset, pixelAtXYOffset + 4);
          }
        }
    });

---

All the functions under impl are not public API and are exposed only for unit testing.

---

Rendering options

filter

A function taking DOM node as argument. Should return true if passed node should be included in the output (excluding node means excluding it's children as well). Not called on the root node.

bgcolor

A string value for the background color, any valid CSS color value.

height, width

Height and width in pixels to be applied to node before rendering.

style

An object whose properties to be copied to node's style before rendering. You might want to check this reference for JavaScript names of CSS properties.

quality

A number between 0 and 1 indicating image quality (e.g. 0.92 => 92%) of the JPEG image. Defaults to 1.0 (100%)

cacheBust

Set to true to append the current time as a query string to URL requests to enable cache busting. Defaults to false

imagePlaceholder

A data URL for a placeholder image that will be used when fetching an image fails. Defaults to undefined and will throw an error on failed images

Browsers

It's tested on latest Chrome and Firefox (49 and 45 respectively at the time of writing), with Chrome performing significantly better on big DOM trees, possibly due to it's more performant SVG support, and the fact that it supports CSSStyleDeclaration.cssText property.

Internet Explorer is not (and will not be) supported, as it does not support SVG <foreignObject> tag

Safari is not supported, as it uses a stricter security model on <foreignObject> tag. Suggested workaround is to use toSvg and render on the server.`

Dependencies

Source

Only standard lib is currently used, but make sure your browser supports:

• Promise
• SVG <foreignObject> tag

Tests

Most importantly, tests depend on:

• js-imagediff, to compare rendered and control images

• ocrad.js, for the parts when you can't compare images (due to the browser rendering differences) and just have to test whether the text is rendered

How it works

There might some day exist (or maybe already exists?) a simple and standard way of exporting parts of the HTML to image (and then this script can only serve as an evidence of all the hoops I had to jump through in order to get such obvious thing done) but I haven't found one so far.

This library uses a feature of SVG that allows having arbitrary HTML content inside of the <foreignObject> tag. So, in order to render that DOM node for you, following steps are taken:

1. Clone the original DOM node recursively

2. Compute the style for the node and each sub-node and copy it to corresponding clone

   • and don't forget to recreate pseudo-elements, as they are not cloned in any way, of course

3. Embed web fonts

   • find all the @font-face declarations that might represent web fonts

   • parse file URLs, download corresponding files

   • base64-encode and inline content as data: URLs

   • concatenate all the processed CSS rules and put them into one <style> element, then attach it to the clone

4. Embed images

   • embed image URLs in <img> elements

   • inline images used in background CSS property, in a fashion similar to fonts

5. Serialize the cloned node to XML

6. Wrap XML into the <foreignObject> tag, then into the SVG, then make it a data URL

7. Optionally, to get PNG content or raw pixel data as a Uint8Array, create an Image element with the SVG as a source, and render it on an off-screen canvas, that you have also created, then read the content from the canvas

8. Done!

Things to watch out for

• if the DOM node you want to render includes a <canvas> element with something drawn on it, it should be handled fine, unless the canvas is tainted - in this case rendering will rather not succeed.

• at the time of writing, Firefox has a problem with some external stylesheets (see issue #13). In such case, the error will be caught and logged.

Authors

Anatolii Saienko, Paul Bakaus (original idea)

License

MIT