Check it out

Download this repo and grab the grade.js file from the /docs/dist folder.

Or install from npm: npm install grade-js

Use the CDN link:

https://npmcdn.com/grade-js/docs/dist/grade.js

Recommended HTML structure:

<!--the gradients will be applied to these outer divs, as background-images-->
<div class="gradient-wrap">
    <img src="./samples/finding-dory.jpg" alt="" />
</div>
<div class="gradient-wrap">
    <img src="./samples/good-dinosaur.jpg" alt="" />
</div>

If you have the grade.js in your project, you can include it with a script tag and initialise it like so:

<script src="path/to/grade.js"></script>
<script type="text/javascript">
    window.addEventListener('load', function(){
        /*
            A NodeList of all your image containers (Or a single Node).
            The library will locate an <img /> within each
            container to create the gradient from.
         */
        Grade(document.querySelectorAll('.gradient-wrap'))
    })
</script>

If you've installed from npm, you can use the library like so:

import Grade from 'grade-js'
// initialise as above

The module this imports will be using ES2015 syntax, so it will need to be transpiled by a build tool, like Babel, and if you are importing the module in this fashion (and using npm), I imagine you're already using a bundling tool, like Webpack or Browserify!

If you want to run this locally, just to test it, you need to serve index.html via a webserver, not just by opening it in a browser, else the browser will throw a security error. I would recommend either live-server (requires Node.js installed on your machine) or if you have Python installed, just run python -m SimpleHTTPServer inside the project root. If you're on Windows, I believe WAMP/Apache is the best way to go.

This plugin utilises the <canvas> element and the ImageData object, and due to cross-site security limitations, the script will fail if one tries to extract the colors from an image not hosted on the current domain, unless the image allows for Cross Origin Resource Sharing.

Enabling CORS on S3

To enable CORS for images hosted on S3 buckets, follow the Amazon guide here; adding the following to the bucket's CORS configuration:

<CORSRule>
 <AllowedOrigin>*</AllowedOrigin>
 <AllowedMethod>GET</AllowedMethod>
</CORSRule>

For all images, you can optionally also include a cross-origin attribute in your image.

<img src="/image.jpg" cross-origin="anonymous"/>

MIT License

Copyright (c) 2016 Ben Howdle

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.