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ripley

Ripley is a fast server-side rendered web UI toolkit with live components.

Create rich webapps without the need for a SPA frontend.

Comparison with SPA

Single Page Appplications are complicated things, ripley is a traditional server side rendered model with websocket enhancement for live parts.

Pros:

No need for an API just for the frontend
No need for client-side state management
No need to wait for large JS download before rendering (or setup complicated SSR for client side apps)
Leverages browser's native routing
No separate backend and frontend build complexity, just use Clojure
Use functions and hiccup to build the UI, like Reagent or other ClojureScript React wrappers

Cons:

Client browser needs constant connection to server
Interaction latency is limited by network conditions
Unsuitable for serverless cloud platforms

Usage

Using ripley is from a regular ring app is easy. You call ripley.html/render-response from a ring handler to create a response that sets up a live context.

The render response takes a root component that will render the page. Any rendered live components are registered with the context and updates are sent to the client if their sources change. Use ripley.html/html macro to output HTML with hiccup style markup.

Live components are rendered with the special :ripley.html/live element. The live component takes a source (which implements ripley.live.protocols/Source) and a component function. The component function is called with the value received from the source.

(def counter (atom 0))

(defn counter-app [counter]
  (h/html
    [:div
      "Counter value: " [::h/live {:source (atom-source counter)
                                   :component #(h/html [:span %])}]
      [:button {:on-click #(swap! counter inc)} "increment"]
      [:button {:on-click #(swap! counter dec)} "decrement"]]))

All event handling attributes (like :on-click or :on-change) are registered as callbacks that are sent via the websocket to the server. See ripley.js namespace for helpers in creating callbacks with more options. You can add debouncing and client side condition and success/failure handlers.

See more details and fully working example in the examples folder.

Sources

The main abstraction for working with live components in ripley is the Source. It provides a way for rendering to get the current value (if available) and allows the live context to listen for changes.

The source value can be an atomic value (like string, number or boolean) or a map or collection. The interpretation of the value of the source if entirely up to the component that is being rendered.

Built-in sources

Ripley provides built-in sources that integrate regular Clojure mechanisms into sources. Built-in sources don't require any external extra dependencies.

You can create sources by calling the specific constructor functions in ripley.live.source namespace or the to-source multimethod.

Type	Description
atom	Regular Clojure atoms. Listens to changes with `add-watch`. See: `use-state`
use-state	Convenient light weight source for per render local state
core.async channel	A core async channel
future	Any future value, if realized by render time, used directly. Otherwise patched in after the result is available.
promise	A promise, if delivered by render time, used directly. Otherwise patched in after the promise is delivered.
computed	Takes one or more input sources and a function. Listens to input sources and calls function with their values to update. See also `c=` convenience macros.
split	Takes a map valued input source and keysets. Distributes changes to sub sources only when their keysets change.

Integration sources

Ripley also contains integration sources that integrate external state into usable sources. Integration sources may need external dependencies (not provided by ripley) see namespace docstring for an integration source in ripley.integration.<type>.

Type	Description
redis	Integrate Redis pubsub channels as sources (uses carmine library)
manifold	Integrate manifold library `deferred` and `stream` as source
xtdb	Integrate XTDB query as an automatically updating source

Working with components

Component functions

In Ripley, components are functions that take in parameters and output HTML fragment as a side-effect. They do not return a value. This is different from normal hiccup, where functions would return a hiccup vector describing the HTML.

Ripley uses the ripley.html/html macro to convert a hiccup style body into plain Clojure that writes HTML. The macro also adds Ripley's internal tracking attributes so components can be updated on the fly.

Any Clojure code can be called inside the body, but take note that return values are discarded. This is a common mistake, forgetting to use the HTML macro in a function and returning a vector. The caller will simply discard it and nothing is output.

Child components

Components form a tree so a component can have child components with their own sources. The children are registered under the parent and if the parent fully rerenders, the children are recursively cleaned up. A component does not need to care if it is at the top level or a child of some other component.

The main consideration comes from the sources used. If the parent component creates per render sources for the children, the children will lose the state when the parent is rerendered.

Dynamic scope

Ripley supports capturing dynamic scope that was in place when a component or callback was created. This can be used to avoid passing in every piece of context to all components (like user information or db connection pools). The set of vars to capture must be configured when calling ripley.html/render-response.