boot-asset-fingerprint

A boot task to fingerprint your assets in order to prevent the browser from caching stale assets.

For a detailed explanation of why fingerprinting assets is a good idea, see the Ruby on Rails asset pipeline documentation. The Google web fundamentals on HTTP caching is also well worth a read.

Essentially, the asset-fingerprint task does 2 things:

• Replaces all asset references in your content files, such as html or css, wrapped in a ${}
• Copies any referenced assets to their fingerprinted location

For example:

<script src="${js/app.js}" type="text/javascript"></script>

becomes

<script src="js/app-0bafd97f3bdd0dcb44ca0c6ea7d106be.js" type="text/javascript"></script>

with js/app-0bafd97f3bdd0dcb44ca0c6ea7d106be.js also committed to the fileset.

All asset reference paths are relative to the root directory where the assets are served. See asset root.

Typical usage

Add the asset-fingerprint task to your release pipeline:

(require '[elit.boot-asset-fingerprint :refer [asset-fingerprint]])

(deftask release []
  (comp (build-jar)
        (asset-fingerprint :extensions [".html" ".css"])))

It's possible to choose the files asset-fingerprint looks at by passing in a list of extensions. Run boot asset-fingerprint -h for the full list of supported options.

To serve up assets in development, call the asset-fingerprint task with skip true:

(deftask dev []
  (comp (watch)
        (asset-fingerprint :skip true)))

Asset root

Specify the asset-root option if your assets are being served out of a subdirectory (such as public). This ensures all of the references to your assets are found in the fileset and updated correctly.

Host assets on a CDN

Asset references can be prefixed with a base URL so that they are ready to be served up by a CDN. You can specify the base URL in the asset-host option.

Attribution

Credit goes to Adam Frey for creating the original boot-asset-fingerprint library.

Copyright and License

Copyright © 2017 English Language iTutoring Limited.

Licensed under the MIT License (see the LICENSE file).