basyura/gist:1082597

## gistfile1.html
<html>
<head>
<script>
var timer_ = null;
var start_ = null;
var background_ = null;
function initialize() {
  background_ = document.body.background;
}
function start() {
  start_ = Date.now();
  timer_ = setInterval(down , 100);
}
function stop() {
  clearTimeout(timer_);
}
function reset() {
  clearTimeout(timer_);
  document.getElementById("timer").innerHTML = 120;
}
function down() {
  var diff = Date.now() - start_;
  var txt  = parseInt(((120000 - diff)  / 1000).toString().split("\.")[0],10);
  if (txt == 0) {
    stop();
    return;
  }
  if (document.body.background != background_) {
    document.body.background = background_;
    back_flg_ = true;
  }
  if (txt % 10 == 0) {
    document.body.background = '';
  }
  document.getElementById("timer").innerHTML = txt;
}
</script>
</head>
<body background="yamiwall.jpeg" bgcolor="black" onload="initialize()">
  <div align="center">
  <input type="button" onclick="start()" value="start">
  <input type="button" onclick="stop()"  value="stop">
  <input type="button" onclick="reset()" value="reset">
  </div>
  <div align="center">
  <span id="timer" style="color:white;font-size:360pt;">120</span>
  </div>
</body>
</html>
	<html>
	<head>
	<script>
	var timer_ = null;
	var start_ = null;
	var background_ = null;
	function initialize() {
	background_ = document.body.background;
	}
	function start() {
	start_ = Date.now();
	timer_ = setInterval(down , 100);
	}
	function stop() {
	clearTimeout(timer_);
	}
	function reset() {
	clearTimeout(timer_);
	document.getElementById("timer").innerHTML = 120;
	}
	function down() {
	var diff = Date.now() - start_;
	var txt = parseInt(((120000 - diff) / 1000).toString().split("\.")[0],10);
	if (txt == 0) {
	stop();
	return;
	}
	if (document.body.background != background_) {
	document.body.background = background_;
	back_flg_ = true;
	}
	if (txt % 10 == 0) {
	document.body.background = '';
	}
	document.getElementById("timer").innerHTML = txt;
	}
	</script>
	</head>
	<body background="yamiwall.jpeg" bgcolor="black" onload="initialize()">
	<div align="center">
	<input type="button" onclick="start()" value="start">
	<input type="button" onclick="stop()" value="stop">
	<input type="button" onclick="reset()" value="reset">
	</div>
	<div align="center">
	<span id="timer" style="color:white;font-size:360pt;">120</span>
	</div>
	</body>
	</html>