spiral.js

function spiral(n) {
  var array = [];
  for (var i = 0; i < n; i++) {
    array[i] = [];
    for (var j = 0; j < n; j++) {
      array[i][j] = 0;
    }
  }

  function stroke(ary, start, last){
    if(typeof start === 'undefined') var start = 0;
    if(typeof last === 'undefined') var last = 0;
    var size = ary.length - start * 2;
    if(size === 1) { 
      ary[start][start] = Math.pow(ary.length, 2);
      return ary;
    }
    if(size === 2) { 
      ary[start][start]     = last + 1;
      ary[start][start+1]   = last + 2;
      ary[start+1][start+1] = last + 3;
      ary[start+1][start]   = last + 4;
      return ary;
    }
    else {
      for(var i=0; i<size; i++)    { ary[0+start][i+start] = i+1+last } 
      for(var i=1; i<size; i++)    { ary[i+start][size-1+start] = i+size+last} 
      for(var i=size-2; i>=0; i--) { ary[size-1+start][i+start] = size*3-2-i+last } 
      for(var i=size-2; i>0; i--)  { ary[i+start][0+start] = size*4-3-i+last }
      stroke(ary, start+1, size*4-4+last);
    }
  }

  stroke(array);
  return array;
}