I turned my phone into a remote deck for my Windows laptop — no cloud, no accounts, one npm start

It started with the dumbest problem in computing: I'm in bed, a movie is playing on my laptop across the room, and pausing it requires physically getting up . Every existing fix annoyed me in some way. Remote desktop apps are overkill and route through someone's cloud. Remote-control apps want accounts, subscriptions, or a native app install. I just wanted my phone to poke my laptop over my own Wi-Fi. So I built LapDeck : one Node.js process on the laptop, a PWA on the phone. Scan a QR code once and your phone becomes an app launcher, touchpad, keyboard, live screen viewer, and media/power remote. MIT licensed, plain JavaScript, no build step. This post is about the four problems that turned out to be more interesting than I expected. The architecture in one line Phone (PWA) ── WebSocket + MJPEG over Wi-Fi ──► Node.js agent (Windows) The agent serves the PWA, exposes a WebSocket for commands, and streams the screen as MJPEG. The protocol is deliberately dumb JSON envelopes — no protobuf, no RPC framework — so a native Android client or a CLI script can speak it in an afternoon. Windows-specific glue (volume, brightness, power, capture) is isolated in src/win/ , so a macOS/Linux port only has to reimplement that layer. Problem 1: mobile keyboards lie to you The obvious way to build a remote keyboard is to listen for keydown and forward key codes. On mobile, this collapses immediately: swipe typing, autocorrect, and IME composition don't emit per-key events. Android will happily tell you every key is keyCode 229 . The fix: stop listening to keys entirely. I keep a hidden input, and on every input event I diff the field's value against the last known state — compute the common prefix, then emit "delete N chars, type this string" to the laptop. Swipe-type a whole word and the laptop receives one clean text insertion. IME composition, autocorrect rewrites, emoji — all just become diffs. The lesson generalizes: on mobile web, treat the text field as the source of truth, n