game-of-life.js

const equals = (a, b) = a[0] == b[0] && a[1] === b[1]

const zone = [-1, 0, 1]

function *around([x, y]) {
    for (const i of zone) {
        for (const j of zone) {
            if (0 === i && 0 === y) {
                continue
            }
            yield [x + i, y + j]
        }
    }
}

const near = (cell, neighbor) => 1 === Math.abs(neighbor[0] - cell[0])
    || 1 === Math.abs(neighbor[1] - cell[1])

const willLive = (n) => 2 == n || 3 == n
const inSet = (cell, cells) => cells.find(item => equals(cell, item))

function next(cells) {
    const newCells = []
    for(let cell of cells) {
        for(const neighbor of around(cell)) {
            if (inSet(neighbor, cells) || inSet(neighbor, newCells)) {
                continue
            }
            let n = 0
            for (const item of cells) {
                if (near(neighbor, item)) {
                    n++
                    if (n > 3) {
                        break
                    }
                }
            }
            if (willLive(n)) {
                newCells.push(neighbor)
            }
        }
    }
    return newCells
}