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@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

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

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

Weekly Installs

391

Repository

vercel-labs/json-render

GitHub Stars

13.3K

First Seen

Feb 5, 2026

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