DOM to Image


Breaking Change Notice

The 3.x release branch included some breaking changes in the very 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

$3

npm install dom-to-image-more

Then load

``javascript
/ 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:

`javascript
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):

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

Save and download a compressed JPEG image:

`javascript
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 elements:

`javascript
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:

`javascript
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:

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

Adjust cloned nodes before/after children are cloned
sample fiddle

`javascript
const adjustClone = (node, clone, after) => {
if (!after && clone.id === 'element') {
clone.style.transform = 'translateY(100px)';
}
return clone;
};

const wrapper = document.getElementById('wrapper');
const blob = domtoimage.toBlob(wrapper, { adjustClonedNode: adjustClone });
`

---

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

---

$3

#### 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.

#### filterStyles

A function taking style propertie name as argument. Should return true if passed propertie
should be included in the output

Sample use:

`javascript
filterStyles(node, propertyName) {
return !propertyName.startssWith('--'); // to filter out CSS variables
}
`

#### adjustClonedNode

A function that will be invoked on each node as they are cloned. Useful to adjust nodes in
any way needed before the conversion. Note that this be invoked before the onclone
callback. The handler gets the original node, the cloned node, and a boolean that says if
we've cloned the children already (so you can handle either before or after)

Sample use:

`javascript
const adjustClone = (node, clone, after) => {
if (!after && clone.id === 'element') {
clone.style.transform = 'translateY(100px)';
}
return clone;
};
`

const wrapper = document.getElementById('wrapper'); const blob =
domtoimage.toBlob(wrapper, { adjustClonedNode: adjustClone});

#### onclone

A function taking the cloned and modified DOM node as argument. It allows to make final
adjustements to the elements before rendering, on the whole clone, after all elements have
been individually cloned. Note that this will be invoked after all the onclone callbacks
have been fired.

The cloned DOM might differ a lot from the original DOM, for example canvas will be
replaced with image tags, some class might have changed, the style are inlined. It can be
useful to log the clone to get a better senses of the transformations.

#### 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.

#### disableInlineImages

Set to true to disable the normal inlining images into the SVG output. This will generate
SVGs that reference the original image files, so they my break if a referenced URL fails.
This is always safe to use when generating a PNG/JPG file because the entire SVG image is
rendered.

#### useCredentialFeatures

Allows optionally setting the useCredentials option if the resource matches a pattern in
the useCredentialFilters array.

#### scale

Scale value to be applied on canvas's ctx.scale() on both x and y axis. Can be used to
increase the image quality with higher image size.

$3

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 the option.corsImg support by passing images With this option, you can setup a
proxy service that will process the requests in a safe CORS context.

2. 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.

3. 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.

4. **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
tag_

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

Dependencies

Uses Object.hasOwn() so needs at least Chrome/Edge 93, Firefox 92, Opera 79. Safari 15.4
or Node 16.9.0

$3

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

- Promise
- SVG tag

$3

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
tag. So, in order to render that DOM node for you, following steps are
taken:

1. Clone the original DOM node recursively

1. 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

1. 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