Terminal game of life

game-of-life.mjs

import readline from 'readline'

const w = process.stdout.columns
const h = process.stdout.rows

const init = () => Array.from({ length: w * h }).map(() => Math.round(Math.random()))

let state = init()

const deindex = (i) => [i % w, Math.floor(i / w)]

// toroidal array - this returns index from arbitrary x/y coordinates
// coordinates can exceeds bounds of width/height, making it toroidal
const index = (dx, dy) => {
  const xmod = dx % w
  const ymod = dy % h
  const x = xmod === 0 ? 0 : (dx < 0 ? w : 0) + xmod
  const y = ymod === 0 ? 0 : (dy < 0 ? h : 0) + ymod
  return x + y * w
}

process.stdout.write('\x1b[2J') // clear screen
process.stdout.write('\x1b[?25l') // hide cursor
process.stdin.setRawMode(true)
readline.emitKeypressEvents(process.stdin)

process.stdin.on('keypress', function (ch, key) {
  if (key && key.ctrl && key.name === 'c') {
    process.stdout.write('\x1b[1;1H') // cursor 0,0
    process.stdout.write('\x1b[2J') // clear screen
    process.stdout.write('\x1b[?25h') // show cursor
    process.stdin.unref()
    clearInterval(tid)
  } else {
    process.stdout.write('\x1b[2J') // clear screen
    state = init()
  }
})

const tid = setInterval(
  () =>
    (state = state.map((cur, i) => {
      const [x, y] = deindex(i)
      const sum = [
        state[index(x - 1, y - 1)],
        state[index(x - 1, y)],
        state[index(x - 1, y + 1)],
        state[index(x, y - 1)],
        state[index(x, y)],
        state[index(x, y + 1)],
        state[index(x + 1, y - 1)],
        state[index(x + 1, y)],
        state[index(x + 1, y + 1)],
      ].reduce((acc, nval) => acc + nval)
      let r = 0
      if (sum === 3) r = 1
      if (sum === 4) r = cur
      if (r !== cur) {
        process.stdout.write(`\x1b[${y + 1};${x + 1}H`) // move cursor
        process.stdout.write(r ? `\u2588` : ' ') // block or space
      }
      return r
    })),
  0
)

Game of life? In MY terminal? It's more likely than you think!