<html><head><script>var Ky=-1;var SHP,TId;var SL=1;var SRL=0;var SR=[];var D=
document;function GBP(){do{var BP=Math.floor(Math.random()*400)}while(GI(BP)!=
"□")return BP}function GS(){var F="";for(i=0;i<20;i++){for(j=0;j<20;j++){
var Id="F"+(i*20+j);F+=((i==0)||(i==19)||(j==0)||(j==19))?"<span id="+Id+
">■</span>":"<span id="+Id+">□</span>"}F+="<br>";}SI("EX",F);SHP=GBP();
SI(SHP,"●");SI(GBP(),"▲");SR[0]=SHP;MS()}function MS(){if(Ky!=-1){SRL++;SHP+=
[-1,-20,1,20][Ky];switch(GI(SHP)){case"●":case"■":clearTimeout(TId);alert(
"GameOver");return;case"▲":SL++;SI(GBP(),"▲");}SR[SRL]=SHP;SI(SHP,"●");SI(SR[
SRL-SL],"□")}TId=setTimeout("MS()",100)}function SI(P,H){D.all["F"+P
].innerHTML=H}function GI(P){return D.all["F"+P].innerHTML}</script></head>
<body onLoad="GS()" onKeyDown="javascript:Ky=event.keyCode-37;" Style="
font-family:monospace"><div id=FEX></div></body></html>

Snake Game(JavaScript)

12行が限界でした。

IE5以上、シフトJIS。
カーソルキーで操作します。