/implementing-command-palettes

name: implementing-command-palettes
description: Use when building Cmd+K command palettes in React - covers keyboard navigation with arrow keys, keeping selected items in view with scrollIntoView, filtering with shortcut matching, and preventing infinite re-renders from reference instability

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