Phoenix App Clip

Mounting React in Phoenix LiveView + transferring data

This skill covers one thing: the seam between a Phoenix LiveView and a React element mounted inside it. Two mechanics:

1. Mounting — a LiveView renders an empty node; a JS hook mounts a React root into it and tears it down cleanly.
2. Data transfer — moving values from Phoenix into React, and events/state from React back to Phoenix.

What the React component is — its UI library, its internal state, its styling — is entirely the user's concern. This skill never prescribes that. It only wires the component into LiveView and the two data channels.

The placeholder node

The LiveView renders an empty node and hands it to a hook. Two attributes matter:

<div
  id={@id}
  phx-update="ignore"
  phx-hook="MountClip"
  data-props={Jason.encode!(@initial)}
>
</div>

• phx-hook="MountClip" names the JS hook that will mount React here.
• phx-update="ignore" is mandatory. Once React owns this subtree, LiveView must not patch it, or React's DOM and LiveView's DOM diffing fight and the UI corrupts. ignore tells LiveView to leave the node's children alone after the first render. (Consequence: you can't stream live updates by changing the node's contents — use the event channel below.)
• data-* attributes carry the initial data from Phoenix into the hook. Encode anything non-trivial with Jason.encode!/1 and parse it in JS.

Mounting — the JS hook

The hook creates a React root on this.el, renders the user's component, and unmounts on destroyed() (LiveView navigations call destroyed(); skipping unmount leaks a root and its listeners every time).

import * as React from 'react';
import { createRoot } from 'react-dom/client';
import { YourComponent } from '@your-scope/your-package';

export const MountClip = {
  MountClip: {
    mounted() {
      this.root = createRoot(this.el);     // store before any async work
      this.props = JSON.parse(this.el.dataset.props || '{}');
      this.render();
    },
    destroyed() {
      this.root?.unmount();                // mandatory
    },
    render() {
      this.root.render(<YourComponent {...this.props} bridge={this.bridge()} />);
    },
  },
};

mounted() may await import(...) the component for code-splitting — just set this.root before the await so destroyed() can find it.

Data transfer — the four channels

You hand the two React→Phoenix functions (and the token, etc.) to the component through a small bridge object — either as a prop (as above) or via a React context the component reads. Both are shown in the templates.

// inside the hook
bridge() {
  return {
    token: this.el.dataset.token,
    pushEvent: (event, payload, onReply) => this.pushEvent(event, payload, onReply),
    // navigation goes through the server's public push_navigate/2
    navigate: (path) => this.pushEvent('navigate', { to: path }),
  };
}

// live updates: server push_event('clip:update', payload) → re-render
mounted() {
  // ...
  this.handleEvent('clip:update', (payload) => {
    this.props = { ...this.props, ...payload };
    this.render();
  });
}

this.el, this.pushEvent, this.handleEvent are all the standard LiveView JS hook API — no extra packages are required.

See references/data-transfer.md for each channel in full, including reply callbacks, JSON-encoding rules, and why live updates must go through events rather than attribute changes.

Workflow

State two identifiers: name (slug/dir) and Name (PascalCase). Then:

1. Have a React component exporting something the hook can render. (This is your code — the skill doesn't dictate it. It just needs to accept props and, if it talks back to the server, use the bridge.)
2. Write the hook assets/js/clips/<name>.js exporting Mount<Name> — copy assets/phoenix/clip_hook.js. Wire the bridge and any handleEvents.
3. Register it in assets/js/hooks.js and pass hooks to your LiveSocket.
4. Render the placeholder from a LiveView / LiveComponent with phx-hook="Mount<Name>", phx-update="ignore", and data-* for initial data — copy assets/phoenix/live.ex, live_component.ex, index.html.heex.
5. Add the route in router.ex.
6. Build & verify: build the JS bundle, open the route, confirm the node is replaced by your component, that initial data-* arrived as props, and that a pushEvent from React lands in handle_event/3.

Templates

Phoenix side (copy into your app):

• assets/phoenix/clip_hook.js — the mount + bidirectional bridge hook (the core of this skill); goes in assets/js/clips/.
• assets/phoenix/live.ex, live_component.ex, index.html.heex — the placeholder node and its LiveView shell, showing data-* initial data, push_event live updates, and handle_event for events from React.

React side (illustrative — your component is your own):

• assets/react/example_component.jsx — a minimal, library-free stub showing how a component consumes props + the bridge. Replace it with your own component.
• assets/react/bridge-context.js — optional context so nested components read token/pushEvent/navigate via useBridge() instead of a prop.

Replace __name__ / __Name__ / __TITLE__ / @your-scope placeholders (legend at the top of each file).