@json-render/svelte

Svelte 5 renderer that converts json-render specs into Svelte component trees.

Quick Start

<script lang="ts">
  import { Renderer, JsonUIProvider } from "@json-render/svelte";
  import type { Spec } from "@json-render/svelte";
  import Card from "./components/Card.svelte";
  import Button from "./components/Button.svelte";

  interface Props {
    spec: Spec | null;
  }

  let { spec }: Props = $props();
  const registry = { Card, Button };
</script>

<JsonUIProvider>
  <Renderer {spec} {registry} />
</JsonUIProvider>

Creating a Catalog

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

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",
    },
  },
});

Defining Components

Components should accept

BaseComponentProps<TProps>

interface BaseComponentProps<TProps> {
  props: TProps; // Resolved props for this component
  children?: Snippet; // Child elements (use {@render children()})
  emit: (event: string) => void; // Fire a named event
  bindings?: Record<string, string>; // Map of prop names to state paths (for $bindState)
  loading?: boolean; // True while spec is streaming
}

<!-- Button.svelte -->
<script lang="ts">
  import type { BaseComponentProps } from "@json-render/svelte";

  interface Props extends BaseComponentProps<{ label: string; variant?: string }> {}
  let { props, emit }: Props = $props();
</script>

<button class={props.variant} onclick={() => emit("press")}>
  {props.label}
</button>

<!-- Card.svelte -->
<script lang="ts">
  import type { Snippet } from "svelte";
  import type { BaseComponentProps } from "@json-render/svelte";

  interface Props extends BaseComponentProps<{ title: string }> {
    children?: Snippet;
  }

  let { props, children }: Props = $props();
</script>

<div class="card">
  <h2>{props.title}</h2>
  {#if children}
    {@render children()}
  {/if}
</div>

Creating a Registry

import { defineRegistry } from "@json-render/svelte";
import { catalog } from "./catalog";
import Card from "./components/Card.svelte";
import Button from "./components/Button.svelte";

const { registry, handlers, executeAction } = defineRegistry(catalog, {
  components: {
    Card,
    Button,
  },
  actions: {
    submit: async (params, setState, state) => {
      // handle action
    },
  },
});

Spec Structure (Element Tree)

The Svelte schema uses the element tree format:

{
  "root": "card1",
  "elements": {
    "card1": {
      "type": "Card",
      "props": { "title": "Hello" },
      "children": ["btn1"]
    },
    "btn1": {
      "type": "Button",
      "props": { "label": "Click me" }
    }
  }
}

Visibility Conditions

Use

visible

• { "$state": "/path" }

  - truthy check

• { "$state": "/path", "eq": value }

  - equality check

• { "$state": "/path", "not": true }

  - falsy check

• { "$and": [cond1, cond2] }

  - AND conditions

• { "$or": [cond1, cond2] }

  - OR conditions

Providers (via JsonUIProvider)

JsonUIProvider

StateContext

ActionContext

VisibilityContext

ValidationContext

Event System

Components use

emit

on

<!-- Button.svelte -->
<script lang="ts">
  import type { BaseComponentProps } from "@json-render/svelte";

  interface Props extends BaseComponentProps<{ label: string }> {}

  let { props, emit }: Props = $props();
</script>

<button onclick={() => emit("press")}>{props.label}</button>

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

Built-in Actions

The

setState

{
  "action": "setState",
  "actionParams": { "statePath": "/activeTab", "value": "home" }
}

Other built-in actions:

pushState

removeState

push

pop

Dynamic Props and Two-Way Binding

Expression forms resolved before your component receives props:

• {"$state": "/state/key"}

  - read from state

• {"$bindState": "/form/email"}

  - read + write-back to state

• {"$bindItem": "field"}

  - read + write-back for repeat items

• {"$cond": <condition>, "$then": <value>, "$else": <value>}

  - conditional value

For writable bindings inside components, use

getBoundProp

<script lang="ts">
  import { getBoundProp } from "@json-render/svelte";
  import type { BaseComponentProps } from "@json-render/svelte";

  interface Props extends BaseComponentProps<{ value?: string }> {}
  let { props, bindings }: Props = $props();

  let value = getBoundProp<string>(
    () => props.value,
    () => bindings?.value,
  );
</script>

<input bind:value={value.current} />

Context Helpers

Preferred helpers:

• getStateValue(path)

  - returns

  { current }

  (read/write)

• getBoundProp(() => value, () => bindingPath)

  - returns

  { current }

  (read/write when bound)

• isVisible(condition)

  - returns

  { current }

  (boolean)

• getAction(name)

  - returns

  { current }

  (registered handler)

Advanced context access:

• getStateContext()

• getActionContext()

• getVisibilityContext()

• getValidationContext()

• getOptionalValidationContext()

• getFieldValidation(ctx, path, config?)

Streaming UI

Use

createUIStream

<script lang="ts">
  import { createUIStream, Renderer } from "@json-render/svelte";

  const stream = createUIStream({
    api: "/api/generate-ui",
    onComplete: (spec) => console.log("Done", spec),
  });

  async function generate() {
    await stream.send("Create a login form");
  }
</script>

<button onclick={generate} disabled={stream.isStreaming}>
  {stream.isStreaming ? "Generating..." : "Generate UI"}
</button>

{#if stream.spec}
  <Renderer spec={stream.spec} {registry} loading={stream.isStreaming} />
{/if}

Use

createChatUI

const chat = createChatUI({ api: "/api/chat-ui" });
await chat.send("Build a settings panel");