nexus

Nexus

Nexus is a small, zero-dependency Clojure(Script) library for declarative action dispatch. The UI is a pure function of state; Nexus makes event handling declarative, minimal, and side-effect-free by separating actions (pure data describing intent) from effects (functions that perform side-effects).

Coordinates: no.cjohansen/nexus {:mvn/version "2025.11.1"}.

Quick Decision: What do you need?

Task	Go to
Add Nexus, write the nexus map, call dispatch	setup-and-api.md
Implement actions, effects, system->state, batching, async	actions-effects-placeholders.md
Use placeholders, dispatch data, nested placeholders	actions-effects-placeholders.md
Use nexus.registry global convenience API	registry.md
Add interceptors, error handling, fail-fast strategy	interceptors.md
Inspect actions in Dataspex, set up action-log	registry.md
Dispatch not working, actions silently dropped, wrong results	anti-patterns.md

Core Mental Model

DOM event / timer / network
  → dispatch [action-vector …]
  → expand actions (pure fns, system snapshot)
  → interpolate placeholders (late-bound dispatch-data)
  → execute effects (impure fns, live system)

• An action is a vector [:keyword arg …] — pure data.
• An action handler is a pure fn (state & args) → [actions].
• An effect handler is an impure fn (ctx system & args) → any.
• system->state converts the live system to an immutable snapshot for action handlers.
• Placeholders [:kw & args] are resolved at dispatch time from dispatch-data.

Two APIs

API	When to use
nexus.core/dispatch nexus system dispatch-data actions	Explicit; pass the nexus map everywhere
nexus.registry/dispatch store dispatch-data actions	Implicit global registry; simpler setup