itch.io

try using this source, it's a little better to understand and has configurable width and height at the top. Unfortunately it's not 551 byte anymore 8p

<canvas id="c" width="532" height="500"><script>
width=58;
height=30;
r=Math.random;
k=e=>{
 if(e){g[b][a]=W;
 e=e.key;
 x=a;
 y=b;
 e=='w'?y--:e=='s'?y++:e=='a'?x--:e=='d'?x++:s;
 if(g[y][x]==R)location.reload();
 if(g[y][x]==W)b=y,a=x}
 g[b][a]='#0f0';
 for(y=b-1; y<b+2; y++){
  for(x=a-1; x<a+2; x++){
   c.fillStyle=g[y][x];
   c.fillRect(x*9,y*9,9,9)
  }}
};
W='#888';
R='#f00';
d=a=b=1;
c=c.getContext('2d');
c.canvas.width=(width+2)*9;
c.canvas.height=(height+2)*9;
g=[];
for(y=0; y<height+2; y++){g[y]=Array(width).fill('#000')};
for(y=1; y<height; y+=2){
 for(x=1; x<width; x+=2){
  g[y][x]=W;
  if(r()>.5&&y<height-2||x>width-3)
  {
   g[y+1][x]=W;
  }
  else
  {
   if(x<width-3)
    g[y][x+1]=W;
  }
  if(y>1&&r()>.9&&d)d=0,g[y][x]=R;
 }
}
g[height-1][width-2]='#000';
onkeypress=k;
k();
</script></canvas>