原生js获取滚动条距离底部距离

距离底部距离 = 可视窗口的高度 - 滚动条距离上面的距离 - 滚动条的高度

//取窗口可视范围的高度 
			function getClientHeight() {
				var clientHeight = 0;
				if(document.body.clientHeight && document.documentElement.clientHeight) {
					var clientHeight = (document.body.clientHeight < document.documentElement.clientHeight) ? document.body.clientHeight : document.documentElement.clientHeight;
				} else {
					var clientHeight = (document.body.clientHeight > document.documentElement.clientHeight) ? document.body.clientHeight : document.documentElement.clientHeight;
				}
				return clientHeight;
			}

//取窗口滚动条高度 
			function getScrollTop() {
				var scrollTop = 0;
				if(document.documentElement && document.documentElement.scrollTop) {
					scrollTop = document.documentElement.scrollTop;
				} else if(document.body) {
					scrollTop = document.body.scrollTop;
				}
				return scrollTop;
			}