Tiny move-based game engine in Node

foo.js

var name = "Bar!";

var dirs = {
  n: [0,1],
  s: [0,-1],
  e: [1,0],
  w: [-1,0]};

function vadd(v1, v2) {
  return v1.map((x,i) => x + v2[i]);
}

function dest(pos, dir) {
  return vadd(pos, dirs[dir]);
}

var gs = {
  player: {
    pos: [0,0]
  },
  nodes: {
    "0,1": {
      description: "A big room with lots of windows",
      items: []
    }
  },
  edges: {
    "0,1,0,2": {
      f: wall
    }
  }
};

function node_desc(gs, nodev) {
  let node = gs.nodes[nodev.toString()];
  if (node && node.description) {
    return node.description;
  } else {
    return "Node " + nodev;
  }
}

function wall(gs, edgev) {
  return "You can't go there";
}

function hall(gs, edgev) {
  // edge is a vector like this [[0,1],[0,2]]
  // update player position be the other position in the edge
  let [p1,p2] = edgev;
  if (gs.player.pos.toString() == p1) {
    gs.player.pos = p2;
  } else {
    gs.player.pos = p1;
  }
  return "You are now in " + node_desc(gs, gs.player.pos);
}

function move(gs, dir) {
  let d = dest(gs.player.pos, dir),
    edgev = [gs.player.pos, d].sort(),
    edge = gs.edges[edgev.toString()];
  if (edge && edge.f) {
    return edge.f(gs, edgev);
  } else {
    return hall(gs, edgev);
  }
}