@json-render/react

React renderer that converts JSON specs into React component trees.

Quick Start

import { defineRegistry, Renderer } from "@json-render/react";
import { catalog } from "./catalog";

const { registry } = defineRegistry(catalog, {
  components: {
    Card: ({ props, children }) => <div>{props.title}{children}</div>,
  },
});

function App({ spec }) {
  return <Renderer spec={spec} registry={registry} />;
}

Creating a Catalog

import { defineCatalog } from "@json-render/core";
import { schema } from "@json-render/react/schema";
import { defineRegistry } from "@json-render/react";
import { z } from "zod";

// Create catalog with props schemas
export const catalog = defineCatalog(schema, {
  components: {
    Button: {
      props: z.object({
        label: z.string(),
        variant: z.enum(["primary", "secondary"]).nullable(),
      }),
      description: "Clickable button",
    },
    Card: {
      props: z.object({ title: z.string() }),
      description: "Card container with title",
    },
  },
});

// Define component implementations with type-safe props
const { registry } = defineRegistry(catalog, {
  components: {
    Button: ({ props }) => (
      <button className={props.variant}>{props.label}</button>
    ),
    Card: ({ props, children }) => (
      <div className="card">
        <h2>{props.title}</h2>
        {children}
      </div>
    ),
  },
});

Spec Structure (Element Tree)

The React schema uses an element tree format:

{
  "root": {
    "type": "Card",
    "props": { "title": "Hello" },
    "children": [
      { "type": "Button", "props": { "label": "Click me" } }
    ]
  }
}

Visibility Conditions

Use visible on elements to show/hide based on state. New syntax: { "$state": "/path" }, { "$state": "/path", "eq": value }, { "$state": "/path", "not": true }, { "$and": [cond1, cond2] } for AND, { "$or": [cond1, cond2] } for OR. Helpers: visibility.when("/path"), visibility.unless("/path"), visibility.eq("/path", val), visibility.and(cond1, cond2), visibility.or(cond1, cond2).

Providers

Provider	Purpose
StateProvider	Share state across components (JSON Pointer paths). Accepts optional store prop for controlled mode.
ActionProvider	Handle actions dispatched via the event system
VisibilityProvider	Enable conditional rendering based on state
ValidationProvider	Form field validation

External Store (Controlled Mode)

Pass a StateStore to StateProvider (or JSONUIProvider / createRenderer) to use external state management (Redux, Zustand, XState, etc.):

import { createStateStore, type StateStore } from "@json-render/react";

const store = createStateStore({ count: 0 });

<StateProvider store={store}>{children}</StateProvider>

// Mutate from anywhere — React re-renders automatically:
store.set("/count", 1);

When store is provided, initialState and onStateChange are ignored.

Dynamic Prop Expressions

Any prop value can be a data-driven expression resolved by the renderer before components receive props:

• { "$state": "/state/key" } - reads from state model (one-way read)
• { "$bindState": "/path" } - two-way binding: reads from state and enables write-back. Use on the natural value prop (value, checked, pressed, etc.) of form components.
• { "$bindItem": "field" } - two-way binding to a repeat item field. Use inside repeat scopes.
• { "$cond": <condition>, "$then": <value>, "$else": <value> } - conditional value
• { "$template": "Hello, ${/name}!" } - interpolates state values into strings
• { "$computed": "fn", "args": { ... } } - calls registered functions with resolved args

{
  "type": "Input",
  "props": {
    "value": { "$bindState": "/form/email" },
    "placeholder": "Email"
  }
}

Components do not use a statePath prop for two-way binding. Use { "$bindState": "/path" } on the natural value prop instead.

Components receive already-resolved props. For two-way bound props, use the useBoundProp hook with the bindings map the renderer provides.

Register $computed functions via the functions prop on JSONUIProvider or createRenderer:

<JSONUIProvider
  functions={{ fullName: (args) => `${args.first} ${args.last}` }}
>

Event System

Components use emit to fire named events, or on() to get an event handle with metadata. The element's on field maps events to action bindings:

// Simple event firing
Button: ({ props, emit }) => (
  <button onClick={() => emit("press")}>{props.label}</button>
),

// Event handle with metadata (e.g. preventDefault)
Link: ({ props, on }) => {
  const click = on("click");
  return (
    <a href={props.href} onClick={(e) => {
      if (click.shouldPreventDefault) e.preventDefault();
      click.emit();
    }}>{props.label}</a>
  );
},

{
  "type": "Button",
  "props": { "label": "Submit" },
  "on": { "press": { "action": "submit" } }
}

The EventHandle returned by on() has: emit(), shouldPreventDefault (boolean), and bound (boolean).

State Watchers

Elements can declare a watch field (top-level, sibling of type/props/children) to trigger actions when state values change:

{
  "type": "Select",
  "props": { "value": { "$bindState": "/form/country" }, "options": ["US", "Canada"] },
  "watch": { "/form/country": { "action": "loadCities" } },
  "children": []
}

Built-in Actions

The setState, pushState, removeState, and validateForm actions are built into the React schema and handled automatically by ActionProvider. They are injected into AI prompts without needing to be declared in catalog actions:

{ "action": "setState", "params": { "statePath": "/activeTab", "value": "home" } }
{ "action": "pushState", "params": { "statePath": "/items", "value": { "text": "New" } } }
{ "action": "removeState", "params": { "statePath": "/items", "index": 0 } }
{ "action": "validateForm", "params": { "statePath": "/formResult" } }

validateForm validates all registered fields and writes { valid, errors } to state.

Note: statePath in action params (e.g. setState.statePath) targets the mutation path. Two-way binding in component props uses { "$bindState": "/path" } on the value prop, not statePath.

useBoundProp

For form components that need two-way binding, use useBoundProp with the bindings map the renderer provides when a prop uses { "$bindState": "/path" } or { "$bindItem": "field" }:

import { useBoundProp } from "@json-render/react";

Input: ({ element, bindings }) => {
  const [value, setValue] = useBoundProp<string>(
    element.props.value,
    bindings?.value
  );
  return (
    <input
      value={value ?? ""}
      onChange={(e) => setValue(e.target.value)}
    />
  );
},

useBoundProp(propValue, bindingPath) returns [value, setValue]. The value is the resolved prop; setValue writes back to the bound state path (no-op if not bound).

BaseComponentProps

For building reusable component libraries not tied to a specific catalog (e.g. @json-render/shadcn):

import type { BaseComponentProps } from "@json-render/react";

const Card = ({ props, children }: BaseComponentProps<{ title?: string }>) => (
  <div>{props.title}{children}</div>
);

defineRegistry

defineRegistry conditionally requires the actions field only when the catalog declares actions. Catalogs with actions: {} can omit it.

Key Exports

Export	Purpose
defineRegistry	Create a type-safe component registry from a catalog
Renderer	Render a spec using a registry
schema	Element tree schema (includes built-in state actions: setState, pushState, removeState, validateForm)
useStateStore	Access state context
useStateValue	Get single value from state
useBoundProp	Two-way binding for $bindState/$bindItem expressions
useActions	Access actions context
useAction	Get a single action dispatch function
useOptionalValidation	Non-throwing variant of useValidation (returns null if no provider)
useUIStream	Stream specs from an API endpoint
createStateStore	Create a framework-agnostic in-memory StateStore
StateStore	Interface for plugging in external state management
BaseComponentProps	Catalog-agnostic base type for reusable component libraries
EventHandle	Event handle type (emit, shouldPreventDefault, bound)
ComponentContext	Typed component context (catalog-aware)