JS 实现导航栏悬停效果(续2)_javascript技巧

//记录导航条原来在页面上的位置
var naviga_offsetTop = 0;

//使导航条，悬停在顶部
function naviga_stay_top(){
//获取滚动距离
var scrollTop = $(document).scrollTop();
//如果向下滚动的距离大于原来导航栏离顶部的距离
//直接将导航栏固定到可视区顶部
if( scrollTop > naviga_offsetTop ){
$("#nav").css({"top": "0px"});
} else {
//如果向下滚动的距离小原来导航栏离顶部的距离，则重新计算导航栏的位置
$("#nav").css({"top": naviga_offsetTop - scrollTop + "px"});
}
}

function onload_function(){
//记录初始状态导航栏的高度
naviga_offsetTop = $("#nav").attr("offsetTop");

//绑定滚动和鼠标事件
$(window).bind("scroll", naviga_stay_top);
$(window).bind("mousewheel",naviga_stay_top);
$(document).bind("scroll", naviga_stay_top);
$(document).bind("mousewheel",naviga_stay_top);
}

$(document).ready( onload_function );

div.main{
width: 800px;
background: #CCC;
margin: 10px auto 0;
position: relative;
}

div.content{
width: 800px;
height: 400px;
background: yellow;
margin: 10px auto 0;
}

div.navigation{
width: 800px;
height: 40px;
background: red;
margin: 0 auto;
top: 400px;
left:50%;
position: fixed;
margin-left:-400px;
}

div.tab{
width: 195px;
height: 40px;
background: blue;
float: left;
margin-left: 5px;
}