@keenmate/svelte-treeview

A high-performance, feature-rich hierarchical tree view component for Svelte 5 with drag & drop support, search functionality, and flexible data structures using LTree.

For AI Agents / LLMs: Comprehensive documentation is available in the ai/ folder with topic-specific files (basic-setup.txt, drag-drop.txt, performance.txt, etc.). Start with ai/INDEX.txt for navigation.

📢 New in v4.7: Per-Node Drop Position Restrictions

[!NOTE] You can now restrict which drop positions (above/below/child) are allowed per node.

Use getAllowedDropPositionsCallback for dynamic logic or allowedDropPositionsMember for server data:

// Files can only have siblings, trash only accepts children
function getAllowedDropPositions(node) {
  if (node.data?.type === 'file') return ['above', 'below'];
  if (node.data?.type === 'trash') return ['child'];
  return undefined; // all positions allowed (default)
}

📢 v4.6: Progressive Flat Rendering

[!NOTE] The tree now uses progressive flat rendering by default for significantly improved performance.

What this means:

• The tree renders immediately with the first batch of nodes (~20 by default)
• Remaining nodes are rendered progressively in subsequent frames
• For large trees (5000+ nodes), you'll see nodes appear over ~100-500ms instead of a single long freeze
• The UI remains responsive during rendering

Configuration options:

<Tree
  {data}
  useFlatRendering={true}   <!-- Default: true (flat mode) -->
  progressiveRender={true}  <!-- Default: true (batched rendering) -->
  initialBatchSize={20}     <!-- First batch size (default: 20) -->
  maxBatchSize={500}        <!-- Maximum batch size cap (default: 500) -->
/>

Exponential batching: The first batch renders 20 nodes instantly, then doubles each frame (20 → 40 → 80 → 160 → 320 → 500...) for optimal perceived performance.

To use the legacy recursive rendering:

<Tree
  {data}
  useFlatRendering={false}  <!-- Uses recursive Node components -->
/>

Recursive mode may be preferred for very small trees or when you need the {#key changeTracker} behavior that recreates all nodes on any change.

🚀 Features

• Svelte 5 Native: Built specifically for Svelte 5 with full support for runes and modern Svelte patterns
• High Performance: Flat rendering mode with progressive loading for 5000+ nodes
• Drag & Drop: Built-in drag and drop with position control (above/below/child), touch support, and async validation
• Tree Editing: Built-in methods for add, move, remove operations with automatic path management
• Search & Filter: Integrated FlexSearch for fast, full-text search capabilities
• Flexible Data Sources: Works with any hierarchical data structure
• Context Menus: Dynamic right-click menus with callback-based generation, icons, disabled states
• Visual Customization: Extensive styling options and icon customization
• TypeScript Support: Full TypeScript support with comprehensive type definitions
• Accessibility: Built with accessibility in mind

📦 Installation

npm install @keenmate/svelte-treeview

🔨 Development Setup

For developers working on the project, you can use either standard npm commands or the provided Makefile (which provides a unified interface for all contributors):

# Using Makefile (recommended for consistency)
make setup      # or make install
make dev

# Or using standard npm commands
npm install
npm run dev

🎨 Importing Styles

The component requires CSS to display correctly. Import the styles in your app:

Option 1: Import SCSS in your main app file

// In your main.js or main.ts
import '@keenmate/svelte-treeview/styles.scss';

Option 2: Import in your Svelte component

<style>
  @import '@keenmate/svelte-treeview/styles.scss';
</style>

Option 3: Use with your build system

If using Vite, Webpack, or similar, you can import the SCSS:

import '@keenmate/svelte-treeview/styles.scss';

⚠️ Performance Warning: Use $state.raw() for Large Datasets

[!WARNING] When passing large arrays (1000+ items) to the Tree component, use $state.raw() instead of $state() to avoid severe performance issues.

Svelte 5's $state() creates deep proxies for all nested objects. With thousands of items, this causes massive overhead during tree operations.

// ❌ SLOW - Each item becomes a Proxy (5000x slower with large datasets)
let treeData = $state<TreeNode[]>([])

// ✅ FAST - Items remain plain objects
let treeData = $state.raw<TreeNode[]>([])

Symptoms of this issue:

• Tree takes 15-90+ seconds to render with thousands of items
• Console shows [Violation] 'message' handler took XXXXms
• Same data loads instantly in isolated test

The array itself remains reactive - only individual items lose deep reactivity (which Tree doesn't need).

🎯 Quick Start

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  
  const data = [
    { path: '1', name: 'Documents', type: 'folder' },
    { path: '1.1', name: 'Projects', type: 'folder' },
    { path: '1.1.1', name: 'Project A', type: 'folder' },
    { path: '1.1.2', name: 'Project B', type: 'folder' },
    { path: '2', name: 'Pictures', type: 'folder' },
    { path: '2.1', name: 'Vacation', type: 'folder' }
  ];
</script>

<Tree
  {data}
  idMember="path"
  pathMember="path"
  displayValueMember="name"
/>

🔧 Advanced Usage

With Custom Node Templates

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  
  const fileData = [
    { path: '1', name: 'Documents', type: 'folder', icon: '📁' },
    { path: '1.1', name: 'report.pdf', type: 'file', icon: '📄', size: '2.3 MB' },
    { path: '2', name: 'Images', type: 'folder', icon: '🖼️' },
    { path: '2.1', name: 'photo.jpg', type: 'file', icon: '🖼️', size: '1.8 MB' }
  ];
</script>

<Tree
  data={fileData}
  idMember="path"
  pathMember="path"
  selectedNodeClass="ltree-selected-bold"
  onNodeClicked={(node) => console.log('Clicked:', node.data.name)}
>
  {#snippet nodeTemplate(node)}
    <div class="d-flex align-items-center">
      <span class="me-2">{node.data.icon}</span>
      <strong>{node.data.name}</strong>
      {#if node.data.size}
        <small class="text-muted ms-2">({node.data.size})</small>
      {/if}
    </div>
  {/snippet}
</Tree>

With Search and Filtering

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  
  let searchText = $state('');
  const data = [/* your data */];
</script>

<input 
  type="text" 
  placeholder="Search..." 
  bind:value={searchText} 
/>

<Tree
  {data}
  idMember="path"
  pathMember="path"
  shouldUseInternalSearchIndex={true}
  searchValueMember="name"
  bind:searchText
/>

With Advanced Search Options

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  import type { SearchOptions } from 'flexsearch';
  
  let treeRef;
  const data = [/* your data */];
  
  // Programmatic search with FlexSearch options
  function performAdvancedSearch(searchTerm: string) {
    const searchOptions: SearchOptions = {
      suggest: true,        // Enable suggestions for typos
      limit: 10,            // Limit results to 10 items  
      bool: "and"           // Use AND logic for multiple terms
    };
    
    const results = treeRef.searchNodes(searchTerm, searchOptions);
    console.log('Advanced search results:', results);
  }
  
  // Programmatic filtering with options
  function filterWithOptions(searchTerm: string) {
    const searchOptions: SearchOptions = {
      threshold: 0.8,       // Similarity threshold
      depth: 2              // Search depth
    };
    
    treeRef.filterNodes(searchTerm, searchOptions);
  }
</script>

<Tree
  bind:this={treeRef}
  {data}
  idMember="path"
  pathMember="path"
  shouldUseInternalSearchIndex={true}
  searchValueMember="name"
/>

<button onclick={() => performAdvancedSearch('document')}>
  Advanced Search
</button>
<button onclick={() => filterWithOptions('project')}>
  Filter with Options
</button>

FlexSearch Options Reference

The searchOptions parameter accepts any options supported by FlexSearch. Common options include:

Option	Type	Description	Example
suggest	boolean	Enable suggestions for typos	{ suggest: true }
limit	number	Maximum number of results	{ limit: 10 }
threshold	number	Similarity threshold (0-1)	{ threshold: 0.8 }
depth	number	Search depth for nested content	{ depth: 2 }
bool	string	Boolean logic: "and", "or"	{ bool: "and" }
where	object	Filter by field values	{ where: { type: "folder" } }

For complete FlexSearch documentation, visit: FlexSearch Options

With Drag & Drop

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';

  let treeRef: Tree<MyNode>;

  const data = [
    { path: '1', name: 'Folder 1', isDraggable: true },
    { path: '1.1', name: 'Item 1', isDraggable: true },
    { path: '2', name: 'Folder 2', isDraggable: true }
  ];

  function onDragStart(node, event) {
    console.log('Dragging:', node.data.name);
  }

  // Same-tree moves are auto-handled - this callback is for notification/custom logic
  function onDrop(dropNode, draggedNode, position, event, operation) {
    console.log(`Dropped ${draggedNode.data.name} ${position} ${dropNode?.data.name}`);
    // position is 'above', 'below', or 'child'
    // operation is 'move' or 'copy' (Ctrl+drag)
  }
</script>

<Tree
  bind:this={treeRef}
  {data}
  idMember="path"
  pathMember="path"
  orderMember="sortOrder"
  dragOverNodeClass="ltree-dragover-highlight"
  onNodeDragStart={onDragStart}
  onNodeDrop={onDrop}
/>

Drop Position Control

When using dropZoneMode="floating" (default), users can choose where to drop:

• Above: Insert as sibling before the target node
• Below: Insert as sibling after the target node
• Child: Insert as child of the target node

Per-Node Drop Position Restrictions

You can restrict which drop positions are allowed per node. This is useful for:

• Trash/Recycle Bin: Only allow dropping INTO (child), not above/below
• Files: Only allow above/below (can't drop INTO a file)
• Folders: Allow all positions (default)

<script lang="ts">
  import { Tree, type DropPosition, type LTreeNode } from '@keenmate/svelte-treeview';

  // Dynamic callback approach
  function getAllowedDropPositions(node: LTreeNode<MyItem>): DropPosition[] | null {
    if (node.data?.type === 'file') return ['above', 'below'];
    if (node.data?.type === 'trash') return ['child'];
    return undefined; // all positions allowed
  }
</script>

<Tree
  {data}
  getAllowedDropPositionsCallback={getAllowedDropPositions}
/>

Or use the member approach for server-side data:

<Tree
  {data}
  allowedDropPositionsMember="allowedDropPositions"
/>

<!-- Where data items have: { allowedDropPositions: ['child'] } -->

When restrictions are applied:

• Glow mode: Snaps to the nearest allowed position
• Floating mode: Only renders buttons for allowed positions

Async Drop Validation

Use beforeDropCallback to validate or modify drops, including async operations like confirmation dialogs:

<script lang="ts">
  async function beforeDrop(dropNode, draggedNode, position, event, operation) {
    // Cancel specific drops
    if (draggedNode.data.locked) {
      return false; // Cancel the drop
    }

    // Show confirmation dialog (async)
    if (position === 'child' && !dropNode.data.isFolder) {
      const confirmed = await showConfirmDialog('Drop as sibling instead?');
      if (!confirmed) return false;
      return { position: 'below' }; // Override position
    }

    // Proceed normally
    return true;
  }
</script>

<Tree
  {data}
  beforeDropCallback={beforeDrop}
  onNodeDrop={onDrop}
/>

Tree Editing

The tree provides built-in methods for programmatic editing:

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';

  let treeRef: Tree<MyNode>;

  // Add a new node
  function addChild() {
    const result = treeRef.addNode(
      selectedNode?.path || '', // parent path (empty = root)
      { id: Date.now(), path: '', name: 'New Item', sortOrder: 100 }
    );
    if (result.success) {
      console.log('Added:', result.node);
    }
  }

  // Move a node
  function moveUp() {
    const siblings = treeRef.getSiblings(selectedNode.path);
    const index = siblings.findIndex(s => s.path === selectedNode.path);
    if (index > 0) {
      treeRef.moveNode(selectedNode.path, siblings[index - 1].path, 'above');
    }
  }

  // Remove a node
  function remove() {
    treeRef.removeNode(selectedNode.path);
  }
</script>

<Tree
  bind:this={treeRef}
  {data}
  idMember="id"
  pathMember="path"
  orderMember="sortOrder"
/>

Note: When using orderMember, the tree automatically calculates sort order values when moving nodes with 'above' or 'below' positions.

With Context Menus

The tree supports context menus with two approaches: callback-based (recommended) and snippet-based.

Callback-Based Context Menus

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  import type { ContextMenuItem } from '@keenmate/svelte-treeview';

  const data = [
    { path: '1', name: 'Documents', type: 'folder', canEdit: true, canDelete: true },
    { path: '1.1', name: 'report.pdf', type: 'file', canEdit: true, canDelete: false },
    { path: '2', name: 'Images', type: 'folder', canEdit: false, canDelete: true }
  ];

  function createContextMenu(node): ContextMenuItem[] {
    const items: ContextMenuItem[] = [];

    // Always available
    items.push({
      icon: '📂',
      title: 'Open',
      callback: () => alert(`Opening ${node.data.name}`)
    });

    // Conditional actions based on node data
    if (node.data.canEdit) {
      items.push({
        icon: '✏️',
        title: 'Edit',
        callback: () => alert(`Editing ${node.data.name}`)
      });
    }

    if (node.data.canDelete) {
      items.push({
        icon: '🗑️',
        title: 'Delete',
        callback: () => confirm(`Delete ${node.data.name}?`) && alert('Deleted!')
      });
    }

    // Divider
    items.push({ isDivider: true });

    // Disabled item example
    items.push({
      icon: '🔒',
      title: 'Restricted Action',
      isDisabled: true,
      callback: () => {}
    });

    return items;
  }
</script>

<Tree
  {data}
  idMember="path"
  pathMember="path"
  contextMenuCallback={createContextMenu}
  contextMenuXOffset={8}
  contextMenuYOffset={0}
/>

Snippet-Based Context Menus

<Tree
  {data}
  idMember="path"
  pathMember="path"
>
  {#snippet contextMenu(node, closeMenu)}
    <div class="context-menu-item" onclick={() => { alert(`Open ${node.data.name}`); closeMenu(); }}>
      📂 Open
    </div>
    <div class="context-menu-divider"></div>
    <div class="context-menu-item" onclick={() => { alert(`Delete ${node.data.name}`); closeMenu(); }}>
      🗑️ Delete
    </div>
  {/snippet}
</Tree>

Context Menu Features

• Dynamic menus: Generate menu items based on node properties
• Icons and dividers: Visual organization and identification
• Disabled states: Context-sensitive menu availability
• Position offset: contextMenuXOffset/contextMenuYOffset for cursor clearance
• Auto-close: Closes on scroll, click outside, or programmatically
• Type safety: Full TypeScript support with ContextMenuItem interface

🎨 Styling and Customization

The component comes with default styles that provide a clean, modern look. You can customize it extensively:

CSS Variables

The component uses CSS custom properties for easy theming:

:root {
  --tree-node-indent-per-level: 0.5rem;  /* Controls indentation for each hierarchy level */
  --ltree-primary: #0d6efd;
  --ltree-primary-rgb: 13, 110, 253;
  --ltree-success: #198754;
  --ltree-success-rgb: 25, 135, 84;
  --ltree-danger: #dc3545;
  --ltree-danger-rgb: 220, 53, 69;
  --ltree-light: #f8f9fa;
  --ltree-border: #dee2e6;
  --ltree-body-color: #212529;
}

Note: The --tree-node-indent-per-level variable controls the consistent indentation applied at each hierarchy level. Each nested level receives this fixed indent amount, creating proper visual hierarchy without exponential indentation growth.

SCSS Variables (if using SCSS)

If you're building the styles from SCSS source, you can override these variables:

// Import your overrides before the library styles
$tree-node-indent-per-level: 1rem;
$tree-node-font-family: 'Custom Font', sans-serif;
$primary-color: #custom-color;

@import '@keenmate/svelte-treeview/styles.scss';

CSS Classes

• .ltree-tree - Main tree container
• .ltree-node - Individual node container
• .ltree-node-content - Node content area
• .ltree-toggle-icon - Expand/collapse icons
• .ltree-selected-* - Selected node styles
• .ltree-dragover-* - Drag-over node styles
• .ltree-draggable - Draggable nodes
• .ltree-context-menu - Context menu styling
• .ltree-drag-over - Applied during drag operations
• .ltree-drop-valid / .ltree-drop-invalid - Drop target validation

Pre-built Selected Node Styles

The component includes several pre-built classes for styling selected nodes:

<Tree
  {data}
  idMember="path"
  pathMember="path"
  selectedNodeClass="ltree-selected-bold"
/>

Available Selected Node Classes:

Class	Description	Visual Effect
ltree-selected-bold	Bold text with primary color	Bold text in theme primary color
ltree-selected-border	Border and background highlight	Solid border with light background
ltree-selected-brackets	Decorative brackets around text	❯ Node Text ❮

Available Drag-over Node Classes:

Class	Description	Visual Effect
ltree-dragover-highlight	Dashed border with success color background	Green dashed border with subtle background
ltree-dragover-glow	Blue glow effect	Glowing shadow effect with primary color theme

Custom Icon Classes

<Tree
  {data}
  idMember="path"
  pathMember="path"
  expandIconClass="custom-expand-icon"
  collapseIconClass="custom-collapse-icon"
  leafIconClass="custom-leaf-icon"
/>

📚 API Reference

Tree Component Props

Core Required Properties

Prop	Type	Required	Description
data	T[]	✅	Array of data objects
idMember	string	✅	Property name for unique identifiers
pathMember	string	✅	Property name for hierarchical paths
sortCallback	(items: T[]) => T[]	✅	Function to sort items

Data Mapping Properties

Prop	Type	Default	Description
treeId	string | null	null	Unique identifier for the tree
parentPathMember	string | null	null	Property name for parent path references
levelMember	string | null	null	Property name for node level
isExpandedMember	string | null	null	Property name for expanded state
isSelectedMember	string | null	null	Property name for selected state
isDraggableMember	string | null	null	Property name for draggable state
isDropAllowedMember	string | null	null	Property name for drop allowed state
allowedDropPositionsMember	string | null	null	Property name for allowed drop positions array
hasChildrenMember	string | null	null	Property name for children existence
isSorted	boolean | null	null	Whether items should be sorted

Display & Search Properties

Prop	Type	Default	Description
displayValueMember	string | null	null	Property name for display text
getDisplayValueCallback	(node) => string	undefined	Function to get display value
searchValueMember	string | null	null	Property name for search indexing
getSearchValueCallback	(node) => string	undefined	Function to get search value
shouldUseInternalSearchIndex	boolean	false	Enable built-in search functionality
initializeIndexCallback	() => Index	undefined	Function to initialize search index
searchText	string (bindable)	undefined	Current search text

Note: When shouldUseInternalSearchIndex is enabled, node indexing is performed asynchronously using requestIdleCallback (with fallback to setTimeout). This ensures the tree renders immediately while search indexing happens during browser idle time, providing better performance for large datasets.

⚠️ Important: For internal search indexing to work, you must:

1. Set shouldUseInternalSearchIndex={true}
2. Provide either searchValueMember (property name) or getSearchValueCallback (function)

Without both requirements, no search indexing will occur.

Performance Tuning:

• indexerBatchSize controls how many nodes are processed per idle callback. Lower values (10-25) provide smoother UI performance but slower indexing, while higher values (50-100) index faster but may cause brief UI pauses. Default: 25.
• indexerTimeout sets the maximum wait time before forcing indexing when the browser is busy. Lower values (25-50ms) ensure more responsive indexing, while higher values (100-200ms) give more time for genuine idle periods. Default: 50ms.

Tree Configuration

Prop	Type	Default	Description
treeId	string | null	auto-generated	Unique identifier for the tree
treePathSeparator	string | null	"."	Separator character for hierarchical paths (e.g., "." for "1.2.3" or "/" for "1/2/3")
selectedNode	LTreeNode<T> (bindable)	undefined	Currently selected node
insertResult	InsertArrayResult<T> (bindable)	undefined	Result of the last data insertion including failed nodes

Behavior Properties

Prop	Type	Default	Description
expandLevel	number | null	2	Automatically expand nodes up to this level
shouldToggleOnNodeClick	boolean	true	Toggle expansion on node click
useFlatRendering	boolean	true	Use flat rendering mode (faster for large trees)
progressiveRender	boolean	true	Progressively render nodes in batches
renderBatchSize	number	50	Number of nodes to render per batch
orderMember	string | null	null	Property name for sort order (enables above/below positioning in drag-drop)
indexerBatchSize	number | null	25	Number of nodes to process per batch during search indexing
indexerTimeout	number | null	50	Maximum time (ms) to wait for idle callback before forcing indexing
shouldDisplayDebugInformation	boolean	false	Show debug information panel with tree statistics and enable console debug logging for tree operations and async search indexing
shouldDisplayContextMenuInDebugMode	boolean	false	Display persistent context menu at fixed position for styling development

Event Handler Properties

Prop	Type	Default	Description
onNodeClicked	(node) => void	undefined	Node click event handler
onNodeDragStart	(node, event) => void	undefined	Drag start event handler
onNodeDragOver	(node, event) => void	undefined	Drag over event handler
getAllowedDropPositionsCallback	(node) => DropPosition[] | null	undefined	Callback returning allowed drop positions per node
beforeDropCallback	(dropNode, draggedNode, position, event, operation) => boolean | { position?, operation? } | Promise<...>	undefined	Async-capable callback to validate/modify drops before they happen
onNodeDrop	(dropNode, draggedNode, position, event, operation) => void	undefined	Drop event handler. Position is 'above', 'below', or 'child'. Operation is 'move' or 'copy'

Visual Styling Properties

Prop	Type	Default	Description
bodyClass	string | null	undefined	CSS class for tree body
selectedNodeClass	string | null	undefined	CSS class for selected nodes
dragOverNodeClass	string | null	undefined	CSS class for nodes being dragged over
expandIconClass	string | null	"ltree-icon-expand"	CSS class for expand icons
collapseIconClass	string | null	"ltree-icon-collapse"	CSS class for collapse icons
leafIconClass	string | null	"ltree-icon-leaf"	CSS class for leaf node icons
scrollHighlightTimeout	number | null	4000	Duration (ms) for scroll highlight animation
scrollHighlightClass	string | null	'ltree-scroll-highlight'	CSS class to apply for scroll highlight effect

Available Slots

Slot	Description
nodeTemplate	Custom node template
treeHeader	Tree header content
treeBody	Tree body content
treeFooter	Tree footer content
noDataFound	No data template
contextMenu	Context menu template

Public Methods

Method	Parameters	Description
expandNodes	nodePath: string	Expand nodes at specified path
collapseNodes	nodePath: string	Collapse nodes at specified path
expandAll	nodePath?: string	Expand all nodes or nodes under path
collapseAll	nodePath?: string	Collapse all nodes or nodes under path
filterNodes	searchText: string, searchOptions?: SearchOptions	Filter the tree display using internal search index with optional FlexSearch options
searchNodes	searchText: string | null | undefined, searchOptions?: SearchOptions	Search nodes using internal search index and return matching nodes with optional FlexSearch options
scrollToPath	path: string, options?: ScrollToPathOptions	Scroll to and highlight a specific node
update	updates: Partial<Props>	Programmatically update component props from external JavaScript
addNode	parentPath: string, data: T, pathSegment?: string	Add a new node under the specified parent
moveNode	sourcePath: string, targetPath: string, position: 'above' | 'below' | 'child'	Move a node to a new location
removeNode	path: string, includeDescendants?: boolean	Remove a node (and optionally its descendants)
getNodeByPath	path: string	Get a node by its path
getChildren	parentPath: string	Get direct children of a node
getSiblings	path: string	Get siblings of a node (including itself)

ScrollToPath Options

Option	Type	Default	Description
expand	boolean	true	Automatically expand parent nodes to make target visible
highlight	boolean	true	Apply temporary highlight animation to the target node
scrollOptions	ScrollIntoViewOptions	{ behavior: 'smooth', block: 'center' }	Native browser scroll options

Usage Example:

// Basic usage - scroll to path with default options
await tree.scrollToPath('1.2.3');

// Advanced usage - custom options
await tree.scrollToPath('1.2.3', {
  expand: false,           // Don't auto-expand parent nodes
  highlight: false,        // Skip highlight animation
  scrollOptions: {         // Custom scroll behavior
    behavior: 'instant',
    block: 'start'
  }
});

Highlight Classes Example:

<!-- Default background highlight -->
<Tree
  {data}
  idMember="path"
  pathMember="path"
  scrollHighlightClass="ltree-scroll-highlight"
  scrollHighlightTimeout={5000}
/>

<!-- Red arrow highlight -->
<Tree
  {data}
  idMember="path"
  pathMember="path"
  scrollHighlightClass="ltree-scroll-highlight-arrow"
  scrollHighlightTimeout={3000}
/>

<!-- Custom highlight class -->
<Tree
  {data}
  idMember="path"
  pathMember="path"
  scrollHighlightClass="my-custom-highlight"
  scrollHighlightTimeout={2000}
/>

Available Built-in Highlight Classes:

• ltree-scroll-highlight - Background glow with blue color (default)
• ltree-scroll-highlight-arrow - Red left arrow indicator

Statistics

The tree provides real-time statistics about the loaded data:

Property	Type	Description
statistics	{ nodeCount: number; maxLevel: number; filteredNodeCount: number; isIndexing: boolean; pendingIndexCount: number }	Returns current node count, maximum depth level, filtered nodes count, indexing status, and pending index count

const { nodeCount, maxLevel, filteredNodeCount, isIndexing, pendingIndexCount } = tree.statistics;
console.log(`Tree has ${nodeCount} nodes with maximum depth of ${maxLevel} levels`);
if (filteredNodeCount > 0) {
  console.log(`Currently showing ${filteredNodeCount} filtered nodes`);
}
if (isIndexing) {
  console.log(`Search indexing in progress: ${pendingIndexCount} nodes pending`);
}

External Updates (Vanilla JavaScript)

The update() method allows you to programmatically update component props from external JavaScript code (outside of Svelte's reactivity system). This is particularly useful for HTML/JavaScript integration or dynamic configuration from non-Svelte code.

// Get reference to the tree component
const treeElement = document.querySelector('#my-tree');

// Update multiple props at once
treeElement.update({
  searchText: 'Production',
  expandLevel: 3,
  shouldDisplayDebugInformation: true,
  data: newDataArray,
  contextMenuXOffset: 10
});

// Update single prop
treeElement.update({ searchText: 'new search' });

// Update data and configuration
treeElement.update({
  data: fetchedData,
  expandLevel: 5,
  selectedNodeClass: 'custom-selected'
});

Updatable Properties: All Tree props can be updated except snippets/templates, including:

• Data and state: data, searchText, selectedNode, expandLevel
• Members: idMember, pathMember, displayValueMember, searchValueMember
• Callbacks: sortCallback, getDisplayValueCallback, onNodeClicked, etc.
• Visual: bodyClass, selectedNodeClass, expandIconClass, etc.
• Context menu: contextMenuCallback, contextMenuXOffset, contextMenuYOffset
• Behavior: shouldToggleOnNodeClick, shouldUseInternalSearchIndex, etc.

Debug Information

Enable debug information to see real-time tree statistics and console logging:

<Tree
  {data}
  idMember="path"
  pathMember="path"
  shouldDisplayDebugInformation={true}
/>

Debug Panel

The visual debug panel shows:

• Tree ID
• Data array length
• Expand level setting
• Node count
• Maximum depth levels
• Filtered node count (when filtering is active)
• Search indexing progress (when indexing is active)
• Currently dragged node

Console Debug Logging

When enabled, the component will log detailed information to the browser console including:

Tree Operations:

• Data mapping and sorting performance metrics
• Node filtering and search operations
• Tree structure changes

Async Search Indexing:

• Indexer initialization with batch size
• Queue management (items added, queue size)
• Batch processing details (timeout status, items processed, timing)
• Indexing completion and progress updates

This provides valuable insights for performance optimization and troubleshooting, especially when working with large datasets or complex search operations.

Events

onNodeClicked(node)

Triggered when a node is clicked.

onNodeDragStart(node, event)

Triggered when drag operation starts.

onNodeDragOver(node, event)

Triggered when dragging over a potential drop target.

beforeDropCallback(dropNode, draggedNode, position, event, operation)

Called before a drop is processed. Can be async for showing dialogs.

• Return false to cancel the drop
• Return { position: 'above'|'below'|'child' } to override position
• Return { operation: 'move'|'copy' } to override operation
• Return true or undefined to proceed normally

onNodeDrop(dropNode, draggedNode, position, event, operation)

Triggered when a node is dropped. For same-tree moves, the tree auto-handles the move and this callback is for notification.

• position: 'above', 'below', or 'child'
• operation: 'move' or 'copy' (Ctrl+drag)

Slots

nodeTemplate

Custom template for rendering node content.

{#snippet nodeTemplate(node)}
  <!-- Your custom node content -->
{/snippet}

contextMenu

Custom context menu template (snippet-based approach).

{#snippet contextMenu(node, closeMenu)}
  <button onclick={() => { /* action */ closeMenu(); }}>
    Action
  </button>
{/snippet}

Context Menu Properties

contextMenuCallback

Function that generates context menu items dynamically.

contextMenuCallback: (node: LTreeNode<T>) => ContextMenuItem[]

Where ContextMenuItem is:

interface ContextMenuItem {
  icon?: string;        // Optional icon (emoji or text)
  title: string;        // Menu item text
  isDisabled?: boolean; // Whether item is disabled
  callback: () => void; // Action to perform
  isDivider?: boolean;  // Render as divider instead of item
}

contextMenuXOffset

Horizontal offset from cursor position (default: 8px).

contextMenuYOffset

Vertical offset from cursor position (default: 0px).

shouldDisplayContextMenuInDebugMode

When enabled, displays a persistent context menu at a fixed position for styling development (default: false).

<Tree
  {data}
  contextMenuCallback={createContextMenu}
  shouldDisplayContextMenuInDebugMode={true}
  shouldDisplayDebugInformation={true}
  contextMenuXOffset={10}
  contextMenuYOffset={5}
/>

Debug Mode Features:

• Shows context menu for the second node (or first if only one exists)
• Positions menu 200px right and 100px down from tree's top-left corner
• Persistent display - no need to right-click repeatedly
• Perfect for CSS styling and position testing
• Works with both callback-based and snippet-based context menus

🏗️ Data Structure

The component expects hierarchical data with path-based organization:

interface NodeData {
  path: string;          // e.g., "1.2.3" for hierarchical positioning
  // ... your custom properties
}

Path Examples

• Root level: "1", "2", "3"
• Second level: "1.1", "1.2", "2.1"
• Third level: "1.1.1", "1.2.1", "2.1.1"

Sorting Requirements

Important: For proper tree construction, your sortCallback must sort by level first to ensure parent nodes are inserted before their children:

const sortCallback = (items: LTreeNode<T>[]) => {
  return items.sort((a, b) => {
    // First, sort by level (shallower levels first)
    const aLevel = a.path.split('.').length;
    const bLevel = b.path.split('.').length;
    if (aLevel !== bLevel) {
      return aLevel - bLevel;
    }

    // Then sort by your custom criteria
    return a.data.name.localeCompare(b.data.name);
  });
};

Why this matters: If deeper level nodes are processed before their parents, you'll get "Could not find parent node" errors during tree construction. Level-first sorting ensures hierarchical integrity and enables progressive rendering for large datasets.

Insert Result Information

The tree provides detailed information about data insertion through the insertResult bindable property:

interface InsertArrayResult<T> {
  successful: number;     // Number of nodes successfully inserted
  failed: Array<{        // Nodes that failed to insert
    node: LTreeNode<T>;  // The processed tree node
    originalData: T;     // The original data object
    error: string;       // Error message (usually "Could not find parent...")
  }>;
  total: number;         // Total number of nodes processed
}

Usage Example

<script lang="ts">
  import { Tree } from '@keenmate/svelte-treeview';
  
  let insertResult = $state();
  
  const data = [
    { id: '1', path: '1', name: 'Root' },
    { id: '1.2', path: '1.2', name: 'Child' },    // Missing parent "1.1"
    { id: '1.1.1', path: '1.1.1', name: 'Deep' } // Missing parent "1.1"
  ];
  
  // Check results after tree processes data
  $effect(() => {
    if (insertResult) {
      console.log(`✅ ${insertResult.successful} nodes inserted successfully`);
      console.log(`❌ ${insertResult.failed.length} nodes failed to insert`);
      
      insertResult.failed.forEach(failure => {
        console.log(`Failed: ${failure.originalData.name} - ${failure.error}`);
      });
    }
  });
</script>

<Tree 
  {data} 
  idMember="id" 
  pathMember="path" 
  displayValueMember="name"
  bind:insertResult
/>

Benefits

• Data Validation: Identify missing parent nodes in hierarchical data
• Debugging: Clear error messages with node paths like "Node: 1.1.1 - Could not find parent node: 1.1"
• Data Integrity: Handle incomplete datasets gracefully
• Search Accuracy: Failed nodes are excluded from search index, ensuring search results match visible tree
• User Feedback: Inform users about data issues with detailed failure information

🚀 Performance

The component is optimized for large datasets:

• Flat Rendering Mode: Single {#each} loop instead of recursive components (default, ~12x faster initial render)
• Progressive Rendering: Batched rendering prevents UI freeze during initial load
• Context-Based Callbacks: Stable function references eliminate unnecessary re-renders
• LTree: Efficient hierarchical data structure
• Async Search Indexing: Uses requestIdleCallback for non-blocking search index building
• Accurate Search Results: Search index only includes successfully inserted nodes
• Search Indexing: Uses FlexSearch for fast search operations

Performance Benchmarks (5500 nodes)

Operation	Time
Initial render	~25ms
Expand/collapse	~100-150ms
Search filtering	<50ms

v4.5+ Performance Improvements

Flat Rendering Mode (default) - Renders all visible nodes in a single loop:

<Tree
  {data}
  useFlatRendering={true}
  progressiveRender={true}
/>

Optimized insertArray algorithm - Fixed O(n²) bottleneck. Now loads 17,000+ nodes in under 100ms.

Performance Logging - Built-in performance measurement for debugging:

import { enablePerfLogging } from '@keenmate/svelte-treeview';
enablePerfLogging();

// Or from browser console:
window.components['svelte-treeview'].perf.enable()

Important: See the $state.raw() warning above - using $state() instead of $state.raw() for tree data can cause 5,000x slowdown!

🤝 Contributing

We welcome contributions! Please see our contributing guidelines for details.

📄 License

MIT License - see LICENSE file for details.

🆘 Support

• GitHub Issues: Report bugs or request features
• Documentation: Full documentation

---

Built with ❤️ by KeenMate