DOM to Image

Breaking Change Notice

The 3.x release branch included some breaking changes in the vary infrequently used ability to configure some utility methods used in this internal processing of dom-to-image-more. As browsers have matured, many of the hacks we're accumulated over the years are not needed, or better ways have been found to handle some edge-cases. With the help of folks like @meche-gh, in #99 we're stripping out the following members:

• .mimes - was the not-very-comprehensive list of mime types used to handle inlining things
• .parseExtension - was a method to extract the extension from a filename, used to guess mime types
• .mimeType - was a method to map file extensions to mime types
• .dataAsUrl - was a method to reassemble a data: URI from a Base64 representation and mime type

The 3.x release branch should also fix more node compatibility and iframe issues.

What is it

dom-to-image-more is a library which can turn arbitrary DOM node, including same origin and blob iframes, into a vector (SVG) or raster (PNG or JPEG) image, written in JavaScript.

This fork of dom-to-image by Anatolii Saienko (tsayen) with some important fixes merged. We are eternally grateful for his starting point.

Anatolii's version was 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.

Moved to 1904labs organization from my repositories 2019-02-06 as of version 2.7.3

Installation

NPM

npm install dom-to-image-more

Then load

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

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);
        }
    }
});

Get a canvas object:

domtoimage.toCanvas(document.getElementById('my-node')).then(function (canvas) {
    console.log('canvas', canvas.width, canvas.height);
});

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

copyDefaultStyles

Set to true to enable the copying of the default styles of elements. This will make the process faster. Try disabling it if seeing extra padding and using resetting / normalizing in CSS. Defaults to true.

Alternative Solutions to CORS Policy Issue

Are you facing a CORS policy issue in your app? Don't worry, there are alternative solutions to this problem that you can explore. Here are some options to consider:

1. Use third-party services like allOrigins. With this service, you can fetch the source code or an image in base64 format from any website. However, this method can be a bit slow.

2. Set up your own API service. Compared to third-party services like allOrigins, this method can be faster, but you'll need to convert the image URL to base64 format. You can use the "image-to-base64" package for this purpose.

3. Utilize server-side functions features of frameworks like Next.js. This is the easiest and most convenient method, where you can directly fetch a URL source within server-side functions and convert it to base64 format if needed.

By exploring these alternative solutions, you can overcome the CORS policy issue in your app and ensure that your images are accessible to everyone.

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

As of this v3 branch chain, the testing jig is taking advantage of the onclone hook to insert the clone-output into the testing page. This should make it a tiny bit easier to track down where exactly the inlining of CSS styles against the DOM nodes is wrong.

Most importantly, tests only depend on:

• 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!

Using Typescript

1. Use original dom-to-image type definition npm install @types/dom-to-image --save-dev

2. Create dom-to-image-more type definition (dom-to-image-more.d.ts)

   declare module 'dom-to-image-more' {
    import domToImage = require('dom-to-image-more');
    export = domToImage;
   }

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

Marc Brooks, Anatolii Saienko (original dom-to-image), Paul Bakaus (original idea), Aidas Klimas (fixes), Edgardo Di Gesto (fixes), 樊冬 Fan Dong (fixes), Shrijan Tripathi (docs), SNDST00M (optimize), Joseph White (performance CSS), Phani Rithvij (test), David DOLCIMASCOLO (packaging), Zee (ZM) @zm-cttae (many major updates), Joshua Walsh @JoshuaWalsh (Firefox issues), Emre Coban @emrecoban (documentation), Nate Stuyvesant @nstuyvesant (fixes)

License

MIT