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feat: add headless mode entrypoint leva/headless (#553)
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‎.changeset/kind-owls-grin.md‎

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---
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"leva": minor
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"demo": patch
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---
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feat(headless): add headless mode

‎demo/src/App.jsx‎

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@@ -16,6 +16,7 @@ import UI from './sandboxes/leva-ui/src/App'
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import Theme from './sandboxes/leva-theme/src/App'
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import CustomPlugin from './sandboxes/leva-custom-plugin/src/App'
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import LevaTransient from './sandboxes/leva-transient/src/App'
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import Headless from './sandboxes/leva-headless/src/App'
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const { styled } = createStitches({
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theme: {
@@ -34,6 +35,7 @@ const Page = styled('div', {
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const links = {
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'leva-minimal': Minimal,
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'leva-headless': Headless,
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'leva-busy': Busy,
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'leva-advanced-panels': AdvancedPanels,
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'leva-scroll': Scroll,

‎demo/src/sandboxes/leva-headless/src/App.tsx‎

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/**
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* Example: Using Leva in Headless Mode
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*
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* This demonstrates how to use Leva's state management without
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* rendering the default HTML UI panel.
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*/
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import React, { useState } from 'react'
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import { useControls as useControlsHeaded } from 'leva'
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import { useControls, useLevaInputs, useLevaInput } from 'leva/headless'
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export default function HeadlessDemo() {
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const [isHeadless, setIsHeadless] = useState(true)
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return (
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<div style={{ padding: 20, fontFamily: 'monospace' }}>
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<h2>Leva Headless Demo</h2>
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<div style={{ marginBottom: 20 }}>
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<button
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onClick={() => setIsHeadless(!isHeadless)}
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style={{
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padding: '10px 20px',
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fontSize: '16px',
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marginBottom: '20px',
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backgroundColor: isHeadless ? '#ff0055' : '#00ff55',
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color: 'white',
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border: 'none',
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borderRadius: '4px',
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cursor: 'pointer',
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}}>
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Switch to {isHeadless ? 'Headed' : 'Headless'} Mode
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</button>
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<p>
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<strong>Current Mode:</strong> {isHeadless ? 'Headless' : 'Headed'}
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</p>
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{!isHeadless && (
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<p style={{ color: '#666', fontSize: '14px' }}>
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<strong>Note:</strong> In Headed mode, the Leva panel should be visible (top-right). The custom UI below
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should disappear. If the panel persists when switching to headless mode, there's a bug.
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</p>
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)}
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</div>
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{isHeadless ? <HeadlessComponent /> : <HeadedComponent />}
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</div>
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)
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}
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function HeadlessComponent() {
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const values = useControls({
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name: 'World',
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count: { value: 0, min: 0, max: 10, step: 1 },
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speed: { value: 1, min: 0.1, max: 5, step: 0.1 },
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color: '#ff0055',
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enabled: true,
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})
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const inputs = useLevaInputs()
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return (
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<>
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<div style={{ marginBottom: 40 }}>
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<h3>Current Values:</h3>
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<pre style={{ background: '#f0f0f0', padding: 10, borderRadius: 4 }}>{JSON.stringify(values, null, 2)}</pre>
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</div>
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<div>
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<h3>Custom UI Built from Metadata:</h3>
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<div style={{ display: 'flex', flexDirection: 'column', gap: 15 }}>
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{inputs.map(({ path }) => (
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<CustomControl key={path} path={path} />
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))}
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</div>
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</div>
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</>
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)
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}
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function HeadedComponent() {
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const values = useControlsHeaded({
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name: 'World',
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count: { value: 0, min: 0, max: 10, step: 1 },
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speed: { value: 1, min: 0.1, max: 5, step: 0.1 },
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color: '#ff0055',
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enabled: true,
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})
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return (
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<div style={{ marginBottom: 40 }}>
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<h3>Current Values:</h3>
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<pre style={{ background: '#f0f0f0', padding: 10, borderRadius: 4 }}>{JSON.stringify(values, null, 2)}</pre>
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<p style={{ marginTop: 20, color: '#666', fontSize: '14px' }}>
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The Leva panel should be visible in the top-right corner. When you switch back to headless mode, this panel
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should disappear completely.
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</p>
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</div>
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)
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}
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// Custom control component that uses the headless input data
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function CustomControl({ path }: { path: string }) {
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const levaInput = useLevaInput(path)
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if (!levaInput) return null
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const { input, set } = levaInput
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// Handle different input types with custom UI
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if ('value' in input) {
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const dataInput = input as any
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return (
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<div style={{ display: 'flex', alignItems: 'center', gap: 10 }}>
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<label style={{ minWidth: 120 }}>{dataInput.label}:</label>
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{dataInput.type === 'NUMBER' && (
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<input
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type="range"
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value={dataInput.value}
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min={dataInput.settings?.min ?? 0}
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max={dataInput.settings?.max ?? 100}
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step={dataInput.settings?.step ?? 1}
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onChange={(e) => set(parseFloat(e.target.value))}
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style={{ flex: 1 }}
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/>
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)}
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{dataInput.type === 'STRING' && (
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<input
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type="text"
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value={dataInput.value}
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onChange={(e) => set(e.target.value)}
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style={{ flex: 1, padding: 5 }}
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/>
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)}
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{dataInput.type === 'BOOLEAN' && (
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<input type="checkbox" checked={dataInput.value} onChange={(e) => set(e.target.checked)} />
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)}
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{dataInput.type === 'COLOR' && (
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<input
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type="color"
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value={dataInput.value}
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onChange={(e) => set(e.target.value)}
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style={{ width: 60, height: 30 }}
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/>
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)}
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<span style={{ minWidth: 60, textAlign: 'right', color: '#666' }}>{JSON.stringify(dataInput.value)}</span>
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</div>
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)
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}
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return null
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}

‎packages/leva/headless/package.json‎

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{
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"main": "dist/leva-headless.cjs.js",
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"module": "dist/leva-headless.esm.js"
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}

‎packages/leva/package.json‎

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"preconstruct": {
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"entrypoints": [
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"index.ts",
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"plugin/index.ts"
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"plugin/index.ts",
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"headless/index.ts"
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]
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},
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"peerDependencies": {

‎packages/leva/src/components/Leva/Leva.tsx‎

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import React, { useEffect } from 'react'
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import { createRoot } from 'react-dom/client'
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import { createRoot, type Root } from 'react-dom/client'
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import { levaStore } from '../../store'
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import { LevaRoot, LevaRootProps } from './LevaRoot'
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let rootInitialized = false
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let rootEl: HTMLElement | null = null
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/**
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* Manages the lifecycle of the global Leva panel, including creation, cleanup,
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* and reference counting to ensure the panel is only removed when no components
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* are using it.
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*/
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class PanelLifecycle {
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private refCount = 0
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private rootEl: HTMLElement | null = null
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private reactRoot: Root | null = null
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private initialized = false
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/**
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* Mounts a new instance of the global panel.
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* Increments reference count and creates the panel if it doesn't exist.
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*/
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mount(): void {
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this.refCount++
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if (!this.initialized) {
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this.createPanel()
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this.initialized = true
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}
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}
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/**
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* Unmounts an instance of the global panel.
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* Decrements reference count and destroys the panel when count reaches zero.
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*/
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unmount(): void {
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this.refCount--
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if (this.refCount === 0 && this.initialized) {
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this.destroyPanel()
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this.initialized = false
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}
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}
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/**
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* Creates the panel DOM element and React root.
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* @private
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*/
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private createPanel(): void {
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if (!this.rootEl) {
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this.rootEl =
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document.getElementById('leva__root') || Object.assign(document.createElement('div'), { id: 'leva__root' })
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if (document.body) {
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document.body.appendChild(this.rootEl)
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this.reactRoot = createRoot(this.rootEl)
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this.reactRoot.render(<Leva isRoot />)
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}
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}
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}
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/**
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* Destroys the panel by unmounting React root and removing DOM element.
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* @private
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*/
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private destroyPanel(): void {
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if (this.rootEl) {
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// Unmount React root
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if (this.reactRoot) {
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this.reactRoot.unmount()
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this.reactRoot = null
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}
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// Remove DOM element
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this.rootEl.remove()
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this.rootEl = null
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}
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}
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/**
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* Gets the current reference count (useful for debugging)
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*/
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getRefCount(): number {
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return this.refCount
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}
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/**
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* Checks if the panel is initialized (useful for debugging)
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*/
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isInitialized(): boolean {
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return this.initialized
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}
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}
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// Singleton instance for managing the global panel lifecycle
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const panelLifecycle = new PanelLifecycle()
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type LevaProps = Omit<Partial<LevaRootProps>, 'store'> & { isRoot?: boolean }
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// uses global store
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export function Leva({ isRoot = false, ...props }: LevaProps) {
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useEffect(() => {
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rootInitialized = true
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// if this panel was attached somewhere in the app and there is already
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// a floating panel, we remove it.
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if (!isRoot && rootEl) {
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rootEl.remove()
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rootEl = null
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}
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return () => {
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if (!isRoot) rootInitialized = false
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// Note: This logic for handling non-root panels remains unchanged
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// as it's separate from the global panel lifecycle
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if (!isRoot && panelLifecycle.isInitialized()) {
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// If this panel was attached somewhere in the app and there is already
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// a floating panel, we would need to handle it here
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// For now, keeping the original behavior
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}
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}, [isRoot])
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/**
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* This hook is used by Leva useControls, and ensures that we spawn a Leva Panel
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* without the user having to put it into the component tree. This should only
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* happen when using the global store
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* @param isGlobalPanel
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* happen when using the global store.
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* @param isGlobalPanel - Whether this is a global panel instance
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*/
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export function useRenderRoot(isGlobalPanel: boolean) {
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useEffect(() => {
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if (isGlobalPanel && !rootInitialized) {
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if (!rootEl) {
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rootEl =
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document.getElementById('leva__root') || Object.assign(document.createElement('div'), { id: 'leva__root' })
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if (document.body) {
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document.body.appendChild(rootEl)
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createRoot(rootEl).render(<Leva isRoot />)
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}
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if (isGlobalPanel) {
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panelLifecycle.mount()
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return () => {
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panelLifecycle.unmount()
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}
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rootInitialized = true
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}
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}, [isGlobalPanel])
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}

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