A full-screen program

A full-screen program changes three things about the terminal and has to change all three back on every way out. With closeout each change registers its own undo:

import { alternateScreen, hideCursor, onExit, rawMode } from 'closeout';

const undo = [rawMode(process.stdin), alternateScreen(process.stdout), hideCursor(process.stdout)];

onExit(() => console.log('session saved'), 'flush');

let frame = 0;
const timer = setInterval(() => {
  frame += 1;
  console.log(`frame ${frame}`);
  if (frame === 2) process.kill(process.pid, 'SIGINT'); // the user presses Ctrl-C
}, 10);

export function quit() {
  clearInterval(timer);
  for (const back of undo) back();
}

frame 1
frame 2
session saved

On a terminal, after session saved is written, the restore phase turns raw mode off, leaves the alternate screen and shows the cursor; then the process dies of SIGINT. In a pipe, as here, there is no terminal to restore and nothing but the program's own lines is written.

Three details carry the weight:

• Order of the undos does not matter. They all go in restore, which runs after every flush and release handler, so saving the session happens on the alternate screen and the terminal comes back last.
• Calling the undos yourself is fine. quit() restores the terminal now and unregisters the exit undos, so a program that quits normally leaves nothing for exit to do. Each undo runs once, whoever asks first.
• Raw mode is only undone if closeout turned it on. If the program's input was already raw when rawMode() was called, somebody else owns that state and it is left alone.

A second Ctrl-CCopy Anchor Link

A user who presses Ctrl-C again while session saved is still being written does not get a broken terminal: the second signal waits for the first shutdown, and the process dies of the first signal once restore has run. terminal-restore.test.ts checks this on a real process for a second SIGINT and for a SIGTERM behind it.

A save that hangsCopy Anchor Link

If saving the session never returns, the deadline stops waiting for it, names it, and still runs restore. Give the handler a label so the line on stderr says what hung:

onExit(saveTheSession, { phase: 'flush', label: 'save-the-session' });