About
Assets squasher is exactly what it says on the tin: it takes an HTML file and replaces all included scripts with just one and the same for stylesheets.
One caveat here, it's meant to be used for single page applications. There you typically have one entry point HTML file which links all the necessary scripts and stylesheets. Like this one:
<!DOCTYPE html>
<html ng-app="app" ng-controller="MainController">
<head>
<script defer src="/bower_components/angular/angular.min.js"></script>
<script defer src="/bower_components/angular-route/angular-route.min.js"></script>
<script defer src="/bower_components/angular-animate/angular-animate.min.js"></script>
<script defer src="/bower_components/angular-ui-bootstrap/dist/ui-bootstrap-tpls-0.11.0.min.js"></script>
<script defer src="/app.js"></script>
<script defer src="/services.js"></script>
<link rel="stylesheet" href="/bower_components/bootstrap/dist/css/bootstrap.min.css">
<link rel="stylesheet" href="/bower_components/font-awesome/css/font-awesome.min.css">
<link rel="stylesheet" href="/app.css">
</head>
<body>
<div ng-view>Loading ...</div>
</body>
</html>
Now let's save it into app.html (I'm assuming that all the assets exist). When you run bundle exec assets-asquasher app.html build.html, you'll get build/build.min.js and its source map, build/build.min.css and also build.html which will look like this:
<!DOCTYPE html>
<html ng-app="app" ng-controller="MainController">
<head>
<script src="/build/build.min.js"></script>
<link rel="stylesheet" href="/build/build.min.css">
</head>
<body>
<div ng-view>Loading ...</div>
</body>
</html>
Why Is It Useful?
On production you want to use a single minified JS file and a single minified CSS file. Why? Because speed has significant impact on conversions. Yes, it's all cached after the first request, but how many times have you closed a web page before it even loaded?
On the other hand in development you want to include each unminified script separately, so the backtraces make sense[1].
Ultimately this the simplest solution: no need to change your code like you'd have to with say RequireJS. No need to define dependencies in an extra file – it's already there!
Installation
# Assuming you have Node.js already installed.
npm -g uglify-js uglifycss
gem install assets-asquasher
Footnotes
[1] Or alternatively you could use one build file with source maps, but then you have to user guard or something to constantly rebuild it.