@bun-win32/user32

Zero-dependency, zero-overhead Win32 User32 bindings for Bun on Windows.

Overview

@bun-win32/user32 exposes the user32.dll exports using Bun's FFI. It provides a single class, User32, which lazily binds native symbols on first use. You can optionally preload a subset or all symbols up-front via Preload().

The bindings are strongly typed for a smooth DX in TypeScript.

Features

• Bun-first ergonomics on Windows 10/11.
• Direct FFI to user32.dll (windows, input, clipboard, monitors, and more).
• In-source docs in structs/User32.ts with links to Microsoft Docs.
• Lazy binding on first call; optional eager preload (User32.Preload()).
• No wrapper overhead; calls map 1:1 to native APIs.
• Strongly-typed Win32 aliases (see types/User32.ts).

Requirements

• Bun runtime
• Windows 10 or later

Installation

bun add @bun-win32/user32

Quick Start

import type { Pointer } from 'bun:ffi';
import User32, { MessageBoxType } from '@bun-win32/user32';

// Helper: UTF-16LE null-terminated string
const encode = (str: string) => Buffer.from(`${str}\0`, 'utf16le');

// Null pointer for optional HWND
const NULL = null as unknown as Pointer;

// Show a message box
User32.MessageBoxW(
  NULL,
  encode('Hello from @bun-win32/user32!').ptr,
  encode('Welcome').ptr,
  MessageBoxType.MB_OK | MessageBoxType.MB_ICONINFORMATION
);

[!NOTE] AI agents: see AI.md for the package binding contract and source-navigation guidance. It explains how to use the package without scanning the entire implementation.

Examples

Run the included examples:

bun run example              # Basic User32 usage
bun run example:mouse        # Mouse stalker demo
bun run example:hotkey       # Hotkey registration demo
bun run example:countdown    # Countdown dialog demo

Notes

• Either rely on lazy binding or call User32.Preload().
• User32 wide-string (*W) functions expect UTF-16LE + null terminator. Use a helper like encode() and pass .ptr.
• Windows only. Bun runtime required.
• SAL types & naming: nullability is in the type — Optional<T> (formally optional, SAL _*opt_) and Nullable<T> (plain [in]/[out] the docs say can be NULL), the null sentinel derived from T (null for pointers LP*/P*, 0n for handles/by-value addresses); direction is in the parameter name — _out (_Out_), _in_out (_Inout_), _In_ bare. See AI.md and the repo AGENTS.md.