Rails Integration

ReActionView supports Rails 7.0 through 8.2 on Ruby 3.2 or newer. It plugs into Action View as a template handler and changes nothing else about how Rails renders.

Rails 8.2 brings Herb to Rails on its own. ReActionView is what makes your existing HTML+ERB templates reactive, and it adds the validators, the overlays, the dev tools and the instrumentation on top.

Template handlers

ReActionView registers a herb template handler, so .html.herb templates always render through Herb::Engine.

With config.intercept_erb = true, it also replaces the handler for .html.erb. Only templates with the html format are intercepted, together with the slots format reactive templates answer with. Mailer text parts, .json.erb, .xml.erb and every other format keep rendering through Rails' own ERB handler.

Templates that ship inside gems are handled separately, so a gem's markup can never break your pages. Templates from gems has the options.

Rails 8.2 and the built-in Herb implementation

Rails 8.2 compiles HTML templates through Herb on its own when an application runs the 8.2 framework defaults, through config.action_view.html_erb_implementation. That covers plain compilation. Enabling intercept_erb on Rails 8.2 adds what Rails does not do on its own, which is the validators and transform visitors, validation modes, the debug tooling, the external template modes for gem templates, and reactive templates.

The two settings compose. When intercept_erb is off, Rails 8.2 compiles your HTML templates through its built-in Herb implementation and ReActionView only handles .html.herb templates. When intercept_erb is on, ReActionView takes over HTML template compilation, and templates it declines, such as gem templates in :skip or :fallback mode, compile through the default ERB implementation instead of the built-in Herb one.

On Rails 8.1 and earlier, intercept_erb remains the way to compile .html.erb templates through Herb at all.

What config.slots adds ^0.6.0

Turning on config.slots registers the slots format with the MIME type application/vnd.herb.slots+json. The client sends its requests in that format, with the browser's states in a Herb-State header, to the same URL the page came from.

Your controller actions answer those requests without changes. ReActionView renders the same template without its layout and returns the page's values as JSON. A controller reads the browser's states with herb_state, which is also available in views. An action that responds to formats explicitly, such as create after a form send, answers with format.slots, as shown in Collections and Forms.

A response to a request that carried Herb-State is marked Cache-Control: no-store, since it depends on the state the browser sent.

Assets

The client and the dev tools ship inside the gem. On importmap-rails, the gem pins reactionview itself. With Sprockets or Propshaft, the gem adds its assets to the asset paths. JavaScript Client covers bundler setups.