body背景图片随窗口大小变动

<script>
	$(window).load(function() {
		$("body").css({"background-size":"100% "+$(document).height()+"px"});
	})
	$(window).resize(function () {
		$("body").css({"background-size":"100% "+$(document).height()+"px"});
	});
</script>

	body{
		background: url(/img/bg.jpg) no-repeat;
		height:100%;
		width:100%;
		overflow: hidden;
		background-size:cover;
	}