implementing-command-palettes

Implementing Command Palettes

Overview

Command palettes (Cmd+K / Ctrl+K) need precise keyboard navigation, scroll behavior, and stable references to avoid re-render loops. This skill covers the mechanical patterns that make command palettes feel responsive.

When to Use

• Building a Cmd+K command palette in React
• Implementing arrow key navigation with visual selection
• Keeping selected items visible during keyboard navigation
• Filtering commands by label text AND keyboard shortcuts
• Experiencing infinite re-renders when commands update

Quick Reference

Feature	Implementation
Arrow navigation	Track selectedIndex, clamp with Math.min/max
Keep in view	scrollIntoView({ block: 'nearest', behavior: 'smooth' })
Shortcut matching	Strip spaces from shortcuts, match against query
Stable icons	Define icon elements outside component
Stable handlers	useCallback + noop constant for disabled states

Keyboard Navigation

Index Management

const [selectedIndex, setSelectedIndex] = useState(0);

useEffect(() => {
  if (!isOpen) return;

  const handleKeyDown = (e: KeyboardEvent) => {
    switch (e.key) {
      case 'ArrowDown':
        e.preventDefault();
        // Clamp to last item
        setSelectedIndex((prev) => Math.min(prev + 1, filteredItems.length - 1));
        break;
      case 'ArrowUp':
        e.preventDefault();
        // Clamp to first item
        setSelectedIndex((prev) => Math.max(prev - 1, 0));
        break;
      case 'Enter':
        e.preventDefault();
        if (filteredItems[selectedIndex]) {
          executeCommand(filteredItems[selectedIndex]);
          close();
        }
        break;
      case 'Escape':
        e.preventDefault();
        close();
        break;
    }
  };

  window.addEventListener('keydown', handleKeyDown);
  return () => window.removeEventListener('keydown', handleKeyDown);
}, [isOpen, filteredItems, selectedIndex, close]);

Key patterns:

• e.preventDefault() stops arrow keys from scrolling the page
• Math.min/max prevents index going out of bounds
• Effect depends on filteredItems so navigation updates when filter changes

Reset Selection on Query Change

<input
  value={query}
  onChange={(e) => {
    setQuery(e.target.value);
    setSelectedIndex(0); // Reset to first item when query changes
  }}
/>

Keeping Selected Item in View

Using Refs Array

const itemRefs = useRef<(HTMLButtonElement | null)[]>([]);

// Scroll effect - runs when selection changes
useEffect(() => {
  const selectedItem = itemRefs.current[selectedIndex];
  if (selectedItem) {
    selectedItem.scrollIntoView({
      block: 'nearest', // Minimal scroll - only scroll if needed
      behavior: 'smooth', // Smooth animation
    });
  }
}, [selectedIndex]);

// Assign refs in render
{
  filteredItems.map((item, index) => (
    <button
      key={index}
      ref={(el) => {
        itemRefs.current[index] = el;
      }}
      className={index === selectedIndex ? 'bg-blue-100' : ''}
    >
      {item.label}
    </button>
  ));
}

Alternative: Single Ref for Selected Item

const selectedItemRef = useRef<HTMLButtonElement>(null);

useEffect(() => {
  if (isOpen && selectedItemRef.current) {
    selectedItemRef.current.scrollIntoView({
      block: 'nearest',
      behavior: 'smooth',
    });
  }
}, [isOpen, selectedIndex]);

// Only assign ref to selected item
<button
  ref={index === selectedIndex ? selectedItemRef : null}
>

Why block: 'nearest'?

• 'nearest' only scrolls if the element is outside the visible area
• 'center' would scroll even when item is already visible, causing jarring movement
• 'start' or 'end' would always align to top/bottom

Filtering with Shortcut Matching

const filteredCommands = commands.filter((command) => {
  const q = query.toLowerCase().trim();
  if (!q) return true;

  // Standard label matching
  if (command.label.toLowerCase().includes(q)) return true;

  // Shortcut matching: "gd" matches "g d", "gb" matches "g b"
  if (command.shortcut) {
    const shortcutNoSpaces = command.shortcut.toLowerCase().replace(/\s+/g, '');
    if (shortcutNoSpaces.startsWith(q) || shortcutNoSpaces.includes(q)) {
      return true;
    }
  }

  // For numbered items (PRs, issues), match by number
  if (command.type === 'pr') {
    const numberMatch = q.match(/^#?(\d+)$/);
    if (numberMatch) {
      return String(command.pr.number).startsWith(numberMatch[1]);
    }
  }

  return false;
});

Why strip spaces from shortcuts? Users type continuously without spaces. Shortcut "g d" should match when user types "gd".

Preventing Re-Render Loops

Command palettes often suffer from infinite re-renders when command objects are recreated every render.

Problem: Unstable References

// BAD: Icons recreated every render
function usePageCommands() {
  const commands = useMemo(
    () => [
      {
        label: 'Sync',
        icon: <RefreshCw size={16} />, // New element every render!
        action: () => onSync(), // New function every render!
      },
    ],
    [onSync]
  ); // Even with deps, icon is new

  useRegisterCommands(commands); // Triggers re-registration → re-render loop
}

Solution: Stable References

// GOOD: Icons defined OUTSIDE component
const refreshIcon = <RefreshCw size={16} />;
const refreshSpinIcon = <RefreshCw size={16} className="animate-spin" />;
const noop = () => {};

function usePageCommands({ onSync, isSyncing }: Props) {
  // Memoize handlers
  const handleSync = useCallback(() => onSync?.(), [onSync]);

  const commands = useMemo(
    () => [
      {
        label: isSyncing ? 'Syncing...' : 'Sync',
        icon: isSyncing ? refreshSpinIcon : refreshIcon, // Stable references
        action: isSyncing ? noop : handleSync, // noop, not undefined
      },
    ],
    [isSyncing, handleSync]
  );

  useRegisterCommands(commands);
}

Label-Based Change Detection

Instead of comparing object references, compare by labels:

export function useRegisterCommands(commands: CommandItem[]) {
  const { registerCommands, unregisterCommands } = useCommandPalette();

  // Create stable ID based on LABELS, not object references
  const commandIds = useMemo(
    () =>
      commands
        .map((c) => {
          if (c.type === 'nav') return `nav:${c.path}`;
          return `action:${c.label}`;
        })
        .sort()
        .join('|'),
    [commands]
  );

  const commandsRef = useRef<CommandItem[]>(commands);
  useEffect(() => {
    commandsRef.current = commands;
  });

  const prevIdsRef = useRef<string>('');

  useEffect(() => {
    // Only register if structure actually changed
    if (commandIds !== prevIdsRef.current) {
      registerCommands(commandsRef.current);
      prevIdsRef.current = commandIds;
      return () => unregisterCommands(commandsRef.current);
    }
  }, [commandIds, registerCommands, unregisterCommands]);
}

Command Type Patterns

type CommandItem =
  | { type: 'action'; label: string; icon?: React.ReactNode; action: () => void; shortcut?: string }
  | { type: 'nav'; label: string; icon?: React.ReactNode; path: string; shortcut?: string }
  | { type: 'file'; file: FileType; label: string; icon?: React.ReactNode }
  | { type: 'pr'; pr: PRType; label: string; icon?: React.ReactNode };

// Execute based on type
function executeCommand(command: CommandItem) {
  switch (command.type) {
    case 'action':
      command.action();
      break;
    case 'nav':
      navigate(command.path);
      break;
    case 'file':
      onFileSelect(command.file);
      break;
    case 'pr':
      navigate(`/repos/${command.owner}/${command.repo}/pulls/${command.pr.number}`);
      break;
  }
}

Common Mistakes

Mistake	Why It Fails	Fix
Icons inside useMemo	New icon element every render	Define icons as constants outside component
Not resetting index on filter	Arrow keys start from wrong position	setSelectedIndex(0) in onChange
block: 'center' in scrollIntoView	Jarring scroll when item already visible	Use block: 'nearest'
Missing e.preventDefault()	Arrow keys scroll page AND move selection	Add preventDefault for ArrowUp/Down
Forgetting cleanup in useEffect	Event listeners accumulate	Return cleanup function
undefined for disabled action	Type error or click does nothing	Use noop constant

Testing Checklist

• Cmd+K opens palette, Escape closes
• Arrow Down moves to next item (stops at last)
• Arrow Up moves to previous item (stops at first)
• Enter executes selected command and closes palette
• Selected item scrolls into view when navigating long lists
• Typing resets selection to first matching item
• Shortcuts like "gd" match commands with shortcut "g d"
• No console errors about re-renders or maximum update depth