Game of Life in pure ES6 in 30 loc

gol_es6_2.js

const near = [[-1,-1], [0, -1], [1, -1],
              [-1, 0],          [1,  0],
              [-1, 1], [0,  1], [1,  1]];
         
const neighbours = ([x, y]) => 
    near.map(([nx,ny]) => [x + nx, y + ny])

//maybe using Symbol can help
Array.prototype.hash = function() {return this.join(',')}

const expand = (gen) => {
    //lookup in array is not needed
    existing = gen.map(x => {return [x.hash(), {pos:x, isLive: true, count:0}]}); 
    return gen.reduce((prev, curr) => { 
        neighbours(curr).map(pos => {        
            const existing = prev.get(pos.hash()); 
            if (existing) 
                existing.count++; //mutation :-(
            else
                prev.set(pos.hash(), {pos: pos, count: 1})
        })
        return prev
    }, new Map(existing));
} 

const rules = ({count, isLive}) => 
    (count === 3 || (isLive && count == 2))

const gol = (gen) => 
    Array.from(expand(gen), x => x[1])
        .filter(rules)
        .map(x => x.pos);    
    
const blinker = [[0,0], [0,1], [0,2]];
const pentomimo = [[-1, 0], [-1, 1], [0, -1], [0, 0], [1, 0]];