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https://github.com/tsayen/dom-to-image

Generates an image from a DOM node using HTML5 canvas
https://github.com/tsayen/dom-to-image

canvas css dom html image javascript raster render svg vector

Last synced: 3 days ago
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Generates an image from a DOM node using HTML5 canvas

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README 

        
# DOM to Image



[![Build Status](https://travis-ci.org/tsayen/dom-to-image.svg?branch=master)](https://travis-ci.org/tsayen/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](https://github.com/pbakaus/domvas)

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



```javascript

/* 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.



```html



  domtoimage.toPng(node)

  //...



```



## 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](https://github.com/eligrey/FileSaver.js/),

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](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/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);

          }

        }

    });

```



* * *



_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](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Properties_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 `` tag_  



_Safari [is not supported](https://github.com/tsayen/dom-to-image/issues/27), as it uses a stricter security model on ` 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](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Promise)  

-   SVG `` tag



### Tests



Most importantly, tests depend on:



-   [js-imagediff](https://github.com/HumbleSoftware/js-imagediff),

    to compare rendered and control images



-   [ocrad.js](https://github.com/antimatter15/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



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 ``

        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](https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image) -

    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