keen_phoenix_svelte

🌐 Live demo & docs: keen-phoenix-svelte.keenmate.dev · Hex · HexDocs

Auto-mount compiled Svelte apps into Phoenix — on both LiveView and plain controller-rendered pages — as self-contained islands.

Write this in a template:

<.svelte name="like" id={"like-#{@id}"} props={%{id: @id, liked: @liked}} />

…and the compiled Svelte app in assets/apps/like/ is mounted into that element, kept in sync with server state, given a context/api/channel/live bridge to the server (plus a bus for island-to-island messaging), and torn down on navigation — no manual <script>/<link> wiring. A configurable placeholder shows while the bundle loads (server-wide default, per-app <:placeholder> override), so there's no flash of empty container.

Svelte is the first-class, tooled path, but the mount boundary is framework-neutral — an island's entry just default-exports (target, opts) => { setProps, destroy }. Because every island mounts through that one contract, there's a single component, <.app> (an optional framework="…" attribute just tags data-framework for debugging). The demo mounts Svelte, Lit, React and vanilla-JS islands through it. <.svelte> remains as a back-compat alias.

New here, or comparing this to live_svelte? Start with Philosophy & comparison — the autonomous-island model, what this deliberately doesn't do, and how it differs from live_svelte.

What's New in v1.0.0-rc.3

• Proxy cache with revalidation — :proxy mode now works for unversioned upstreams — Registered proxied bundles are cached in ETS and revalidated rather than pinned forever: a stale entry triggers a single-flight conditional GET (If-None-Match/If-Modified-Since), so a 304 keeps the bytes and a 200 swaps them, with concurrent requests collapsed into one upstream fetch. Freshness follows the upstream's Cache-Control/ETag, falling back to a :ttl (default 5 min) — so a bare cdn/app.js with no version in its URL is re-checked on a cadence instead of cached for a year.
• End-to-end conditional-request chain — The proxy forwards an ETag (synthesizing a weak one when the origin ships none) and answers the browser's If-None-Match with a 304, so browser → Phoenix → origin all revalidate cheaply. This replaces the old fixed 1-year immutable header; a per-app immutable: true opts truly-versioned URLs back into it.
• Bounded proxy memory — Cache entries upsert by URL (refreshes never grow the table) and a periodic sweep evicts URLs no longer in the registry, so a rotating DB-driven app registry stays bounded to its working set.
• Renamed to speak "app", not "island" — KeenPhoenixSvelte.IslandProxy → KeenPhoenixSvelte.Apps.Proxy, config :island_provider → :app_provider (which now also accepts a 2-arity conditional-fetch form), and the proxy-path default /keen-islands → /apps (it shares the base_path prefix). Update your router forward.
• Package metadata / links — corrected the :source_url casing, added homepage_url, and a Website link to the live demo.

What's New in v1.0.0-rc.2

• Framework-neutral <.app> — one component mounts any island — Every island mounts through the same (target, opts) => { setProps, destroy } contract, so there is now a single app/1 component regardless of whether the bundle is Svelte, Lit, React, or hand-written vanilla JS. An optional framework attribute just emits an informational data-framework tag. <.svelte> remains as a back-compat alias for the rc.1 name.
• Placeholder / loader — no flash of empty container — <.app> renders a placeholder that the client clears the instant the bundle mounts (after the fetch, so it stays visible the whole time). Resolution is a per-call <:placeholder> slot › the server-wide config :keen_phoenix_svelte, :placeholder › a built-in, dependency-free skeleton. The server default accepts an HTML string, a function, {mod, fun}, or false to disable.
• Event bus — island-to-island messaging without the server — A bus joins the app boundary: a page-wide, client-side pub/sub (emit/on/once) over a DOM EventTarget, wired into both the LiveView hook and mountStatic(), so independent islands coordinate without a round-trip and without importing each other.
• External apps — a registry with :direct/:proxy delivery — KeenPhoenixSvelte.Apps registers islands whose bundle lives elsewhere (a CDN, another deploy); <.runtime> emits a name → url manifest and AppsManager.resolve/1 loads them. Pick :direct (browser imports the CDN URL) or :proxy (Phoenix fetches and re-serves same-origin via KeenPhoenixSvelte.Apps.Proxy — no CORS, CSP 'self').
• Example reworked into "KeenSpace" — the demo is now a Teams-style workspace that doubles as reference code: chat over channel + Presence, a video catalogue over the REST helper, a calendar over context.tokens, a bus-driven activity toast, simulated i18n, a plain (non-LiveView) route, and Lit/React/vanilla islands alongside the Svelte ones.

How it works

Two cooperating halves:

• Elixir — <.app> renders a hook-bound <div> (phx-update="ignore", data-app, JSON data-props); <KeenPhoenixSvelte.runtime> emits the page context.
• JS — the KeenSvelte hook mounts the island inside a LiveView and AppsManager lazily import()s /apps/<name>/main.mjs (or a registered URL); mountStatic() mounts islands on plain pages. Only the bundles on a page are fetched — and any framework's bundle mounts through the same (target, opts) => { setProps, destroy } contract.

phx-update="ignore" keeps LiveView out of the Svelte-owned subtree; the hook drives mount / prop-update / teardown across live navigation.

Unlike live_svelte, this is the island model — no ~V sigil, no server-rendered slots, no SSR Node runtime.

Install

{:keen_phoenix_svelte, "~> 1.0"}

Plus the npm package @keenmate/phoenix_svelte and a Svelte/Vite toolchain. Full steps in Installation & setup.

Documentation

• Installation & setup — wire the library into your app
• Authoring apps — folder layout, the mount contract, Svelte 5 & 4
• Server communication — runtime context, live, api, channel, bus
• External apps (CDN, direct vs proxy) — load islands from elsewhere, and the :direct/:proxy delivery modes

A complete, runnable demo (the like app on a LiveView route and a plain route, plus a channel) lives in the example/ app.

Versioning

keen_phoenix_svelte is a dual package: the Hex library keen_phoenix_svelte and the npm package @keenmate/phoenix_svelte are released in lockstep at the same version — install matching versions of both. The Elixir side renders the component + hook wiring; the npm side supplies the client runtime (the KeenSvelte hook, AppsManager, the api/channel helpers, and the Vite build helper).

License

MIT.