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    0.0.8 • Public • Published


    Caldera is a server-side execution environment for React. Think of it as the Node.js analog to Phoenix LiveView — all of the application logic (including rendering) runs on the server, and DOM updates are sent to the client in real-time.

    This allows developers to rapidly build interactive and multiplayer applications without developing boilerplate around RPC layers (REST/GraphQL/gRPC) and messaging primitives (WebSockets/subscriptions/etc).

    Because it's built on top of the React reconciler, it's compatible with (currently, a reasonably useful subset of) the existing React API. See what's currently included and what's to come for updates.


    Run npm install caldera to install Caldera.


    A simple example (chat room) to get started:

    import React, { useState } from "react";
    import { renderCalderaApp, makeSharedResource, useSharedState } from "caldera";
    import fs from "fs";
    const DATA_PATH = "messages.json";
    const messagesResource = makeSharedResource(
      // Load initial messages
        ? JSON.parse(fs.readFileSync(DATA_PATH, "utf-8"))
        : []
    const usePersistedMessages = () => {
      // Basic shared state, synced with all clients
      const [messages, setMessages] = useSharedState(messagesResource);
      return [
        // Persist to disk (in prod, use a database)
        (newMessages) => {
          fs.writeFileSync(DATA_PATH, JSON.stringify(newMessages));
    const App = () => {
      const [messages, setMessages] = usePersistedMessages();
      // local state, persisted across client reconnects
      const [draftMsg, setDraftMsg] = useState("");
      return (
          <h1>Chat Room!</h1>
          {messages.map((message, i) => (
            <div key={i}>{message}</div>
            onSubmit={(e) => {
              setMessages([...messages, draftMsg]);
              onChange={(e) => setDraftMsg(e.target.value)}
            <button type="submit">Submit</button>
    renderCalderaApp(<App />, { port: 4000 });

    Install Babel by running npm install @babel/core @babel/node @babel/preset-react.

    Then, run the app using babel-node --presets @babel/preset-react index.jsx.

    A few other examples here demonstrate features like shared state, database usage, and session persistence.


    [Work in progress]

    The caldera package provides the following top-level exports:

    • Head: A React component that renders its children into the page's <head />
    • renderCalderaApp: A function that takes in a React element, and runs the Caldera server on port 8080
    • makeSharedResource: Creates a shared resource suitable for use in useSharedState and useSharedReducer
    • useSharedState/useSharedReducer: Shared equivalents to the useState and useReducer hooks that are initialized with the current value of the passed in resource, and trigger rerenders in all other call sites upon updating
    • useHistory/useLocation - hooks that enable routing functionality

    What works

    • Basic form inputs (text fields/areas, checkboxes, selects, radio buttons)
    • Basic event listeners (onclick/onchange/onsubmit/onfocus/onblur/keyevents)
    • CSS and other head tags (via <Head />)
    • Basic input reconciliation (currently implemented via debounce)
    • Shared state and reducer hooks
    • State serialization and restore + state "forking" whenever a user opens a new client

    What's being worked on

    • More events (ondragstart, intersection observers)
    • <input type="file"> support
    • Better, diff-based input reconciliation

    Future plans

    • Proper versioning for state serialization
      • This will allow support for upgrading the server in-place, while retaining certain parts of the client state
    • Support for selectively rendering arbitrary React components on the client




    npm i caldera

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