gen() in functions.js
function gen() {
  var temp=[];
  for (var id=0;id<1600;id++) temp[id]=0;
  for (var row=1;row<39;row++) {
    for (var col=1;col<39;col++) {
      var n=neighbours(row,col);
      var id=rc2id(row,col);
      var v=g_squares[id];
      if (v==0) { // dead
        if (n==3) v=1;
      } else { // alive
        if (n<2) v=0;
        if (n>3) v=0;
      }
      temp[id]=v;
    }
  }
  for (var id=0;id<1600;id++) {
    g_squares[id]=temp[id];
  }
}

Looks good but how do we know it works?

My plan is to test using a very well know pattern called the glider - you'll see why in a moment.

But how to get this pattern onto our grid? Think about it before looking at the next page.