Implementation of a non-standard "x-sri-fallback" attribute for use with Subresource Integrity.
Example usage:
<script
src='https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js'
x-sri-fallback='/jquery.min.js'
integrity='sha256-ImQvICV38LovIsvla2zykaCTdEh1Z801Y+DSop91wMU='
crossorigin='anonymous'
></script>
<link
rel='stylesheet'
href='https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css'
x-sri-fallback='/bootstrap.min.css'
integrity='sha256-8EtRe6XWoFEEhWiaPkLawAD1FkD9cbmGgEy6F46uQqU='
crossorigin='anonymous'
></link>
In the event that the resource located at the src or href fails to validate against the specified hash, the backup resource at x-sri-fallback will be fetched and validated against the same hash prior to its execution.
Browser compatibility: sri-fallback will work in any browser with MutationObserver support. For older browsers, you'll need a polyfill like this one.