The Asset Pipeline - Ruby on Rails Guides - 0 views
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provides a framework to concatenate and minify or compress JavaScript and CSS assets
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adds the ability to write these assets in other languages and pre-processors such as CoffeeScript, Sass and ERB
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invalidate the cache by altering this fingerprint
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Rails 4 automatically adds the sass-rails, coffee-rails and uglifier gems to your Gemfile
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reduce the number of requests that a browser makes to render a web page
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Starting with version 3.1, Rails defaults to concatenating all JavaScript files into one master .js file and all CSS files into one master .css file
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In production, Rails inserts an MD5 fingerprint into each filename so that the file is cached by the web browser
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The technique sprockets uses for fingerprinting is to insert a hash of the content into the name, usually at the end.
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asset minification or compression
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The sass-rails gem is automatically used for CSS compression if included in Gemfile and no config.assets.css_compressor option is set.
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Supported languages include Sass for CSS, CoffeeScript for JavaScript, and ERB for both by default.
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When a filename is unique and based on its content, HTTP headers can be set to encourage caches everywhere (whether at CDNs, at ISPs, in networking equipment, or in web browsers) to keep their own copy of the content
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asset pipeline is technically no longer a core feature of Rails 4
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Rails uses for fingerprinting is to insert a hash of the content into the name, usually at the end
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With the asset pipeline, the preferred location for these assets is now the app/assets directory.
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Fingerprinting is enabled by default for production and disabled for all other environments
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The files in app/assets are never served directly in production.
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Paths are traversed in the order that they occur in the search path
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You should use app/assets for files that must undergo some pre-processing before they are served.
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By default .coffee and .scss files will not be precompiled on their own
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app/assets is for assets that are owned by the application, such as custom images, JavaScript files or stylesheets.
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lib/assets is for your own libraries' code that doesn't really fit into the scope of the application or those libraries which are shared across applications.
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vendor/assets is for assets that are owned by outside entities, such as code for JavaScript plugins and CSS frameworks.
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Any path under assets/* will be searched
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By default these files will be ready to use by your application immediately using the require_tree directive.
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By default, this means the files in app/assets take precedence, and will mask corresponding paths in lib and vendor
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Sprockets uses files named index (with the relevant extensions) for a special purpose
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Rails.application.config.assets.paths
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causes turbolinks to check if an asset has been updated and if so loads it into the page
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if you add an erb extension to a CSS asset (for example, application.css.erb), then helpers like asset_path are available in your CSS rules
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If you add an erb extension to a JavaScript asset, making it something such as application.js.erb, then you can use the asset_path helper in your JavaScript code
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The asset pipeline automatically evaluates ERB
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data URI — a method of embedding the image data directly into the CSS file — you can use the asset_data_uri helper.
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Sprockets will also look through the paths specified in config.assets.paths, which includes the standard application paths and any paths added by Rails engines.
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image_tag
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the closing tag cannot be of the style -%>
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asset_data_uri
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app/assets/javascripts/application.js
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sass-rails provides -url and -path helpers (hyphenated in Sass, underscored in Ruby) for the following asset classes: image, font, video, audio, JavaScript and stylesheet.
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Rails.application.config.assets.compress
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In JavaScript files, the directives begin with //=
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The require_tree directive tells Sprockets to recursively include all JavaScript files in the specified directory into the output.
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manifest files contain directives — instructions that tell Sprockets which files to require in order to build a single CSS or JavaScript file.
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You should not rely on any particular order among those
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Sprockets uses manifest files to determine which assets to include and serve.
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the family of require directives prevents files from being included twice in the output
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which files to require in order to build a single CSS or JavaScript file
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Directives are processed top to bottom, but the order in which files are included by require_tree is unspecified.
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In JavaScript files, Sprockets directives begin with //=
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If require_self is called more than once, only the last call is respected.
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require directive is used to tell Sprockets the files you wish to require.
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You need not supply the extensions explicitly. Sprockets assumes you are requiring a .js file when done from within a .js file
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paths must be specified relative to the manifest file
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require_directory
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Rails 4 creates both app/assets/javascripts/application.js and app/assets/stylesheets/application.css regardless of whether the --skip-sprockets option is used when creating a new rails application.
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The file extensions used on an asset determine what preprocessing is applied.
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app/assets/stylesheets/application.css
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Additional layers of preprocessing can be requested by adding other extensions, where each extension is processed in a right-to-left manner
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require_self
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use the Sass @import rule instead of these Sprockets directives.
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Keep in mind that the order of these preprocessors is important
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In development mode, assets are served as separate files in the order they are specified in the manifest file.
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when these files are requested they are processed by the processors provided by the coffee-script and sass gems and then sent back to the browser as JavaScript and CSS respectively.
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css.scss.erb
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js.coffee.erb
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Keep in mind the order of these preprocessors is important.
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By default Rails assumes that assets have been precompiled and will be served as static assets by your web server
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with the Asset Pipeline the :cache and :concat options aren't used anymore
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Assets are compiled and cached on the first request after the server is started
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RAILS_ENV=production bundle exec rake assets:precompile
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Debug mode can also be enabled in Rails helper methods
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If you set config.assets.initialize_on_precompile to false, be sure to test rake assets:precompile locally before deploying
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By default Rails assumes assets have been precompiled and will be served as static assets by your web server.
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a rake task to compile the asset manifests and other files in the pipeline
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RAILS_ENV=production bin/rake assets:precompile
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a recipe to handle this in deployment
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links the folder specified in config.assets.prefix to shared/assets
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config/initializers/assets.rb
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The initialize_on_precompile change tells the precompile task to run without invoking Rails
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The X-Sendfile header is a directive to the web server to ignore the response from the application, and instead serve a specified file from disk
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the jquery-rails gem which comes with Rails as the standard JavaScript library gem.
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Possible options for JavaScript compression are :closure, :uglifier and :yui
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concatenate assets
