dom-to-image README

The project's README from github.com/tsayen/dom-to-image. As one markdown file: README.md.

DOM to Image

Build Status

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:

Tests

Most importantly, tests depend on:

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

Authors

Anatolii Saienko, Paul Bakaus (original idea)

License

MIT

dom-to-image (tsayen/dom-to-image)

Searching Database…

10.8K ·GitHub
Dom-to-image
What is this?dom-to-image is a JavaScript library that turns any DOM node into an image — either a vector SVG or a raster PNG/JPEG — rendered with HTML5 canvas.
Is this a standalone app or a library I add to my own project?It is a client-side JavaScript library you install via npm or Bower and call from your own code; it has no server component.
How do I add it to a project?Install via 'npm install dom-to-image' or 'bower install dom-to-image', then include src/dom-to-image.js or dist/dom-to-image.min.js, which exposes a global domtoimage variable with functions like toPng, toJpeg, toSvg and toPixelData.
Does it need any external library like jQuery or FileSaver to work?No runtime dependency beyond standard browser features — your browser just needs to support Promise and the SVG tag. FileSaver is only mentioned as an optional helper for downloading the resulting blob.
Does it work in all browsers?It's tested on Chrome and Firefox only; Internet Explorer isn't supported because it lacks the SVG foreignObject tag, and Safari isn't supported due to its stricter security model for that tag.
Who would use this, and what can go wrong?Front-end developers who need to export a page section as an image (e.g. for sharing or downloading); watch out for tainted canvases inside the DOM node (export will fail) and some external stylesheet issues in Firefox.
How does it actually render the DOM as an image?It clones the DOM node, recomputes and copies computed styles (including pseudo-elements), inlines web fonts and background images as base64 data URLs, serializes everything to XML inside an SVG foreignObject, and then optionally draws that SVG onto an off-screen canvas to produce PNG/JPEG/pixel data.
Can I customize the output, like background color or image quality?Yes — rendering options include bgcolor, height/width, a style object, JPEG quality (0-1), cacheBust for avoiding cached images, and a filter function to exclude specific nodes.
What if an image inside the DOM fails to load during export?You can set the imagePlaceholder option to a data URL that will be used as a fallback; otherwise it throws an error on failed images.
Why build this instead of a server-side screenshot tool?It renders entirely in the browser using SVG's ability to embed arbitrary HTML, avoiding the need for a server-rendering service just to capture a snippet of a page.
What are similar projects?html2canvas, anime, qrcodejs, snabbdom, DOMPurify, satori, jquery, svg.js
Which topics is it in?render, client-side, vector, dom, screenshot, image, canvas, svg, css, browser, html, web-development
Creator
tsayen
Size
9.5 MB
Stars
10.8K
Updated
CommitJun 10
Age
11y
Commits · 90 Days