var naviga_offsetTop = 0
var naviga_offsetLeft = 0
//IE7不识别getElementsByClassName，为了兼容自定义一个
function my_getElementsByClassName(class_name) {
var el = []
//获取所有元素
_el = document.getElementsByTagName('*')
//通过className刷选
for (var i=0i<_el.lengthi++ ) {
if (_el[i].className == class_name ) {
el[el.length] = _el[i]
}
}
return el
}
//导航条，悬停在顶部
function naviga_stay_top(){
var a_navigation_bar = []
if(document.getElementsByClassName){//Chrome, FF
a_navigation_bar = document.getElementsByClassName("navigation")
} else {//IE
a_navigation_bar = my_getElementsByClassName("navigation")
}
var scrollTop = document.body.scrollTop || document.documentElement.scrollTop
document.title = 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 ){
a_navigation_bar[0].style.top = 0 + "px"
} 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
a_navigation_bar[0].style.top = (naviga_offsetTop - scrollTop) + "px"
}
}
//给导航条上四个tab，加上点击事件。
window.onload=function(){
var a_tabs = []
if( document.getElementsByClassName ){//Chrome, FF
a_tabs = document.getElementsByClassName("tab")
}else{ //IE
a_tabs = my_getElementsByClassName("tab")
}
var a_contents = []
if( document.getElementsByClassName ){//Chrome, FF
a_contents = document.getElementsByClassName("content")
}else{//IE
a_contents = my_getElementsByClassName("content")
}
//获取offsetLeft，即导航栏离左边框的距离
var a_main_div = []
if( document.getElementsByClassName ){//Chrome, FF
a_main_div = document.getElementsByClassName("main")
}else{ //IE
a_main_div = my_getElementsByClassName("main")
}
naviga_offsetLeft = a_main_div[0].offsetLeft
a_tabs[0].onclick=function(){
window.scrollTo(0, a_contents[2].offsetTop)
}
a_tabs[1].onclick=function(){
window.scrollTo(0, a_contents[3].offsetTop)
}
a_tabs[2].onclick=function(){
window.scrollTo(0, a_contents[4].offsetTop)
}
a_tabs[3].onclick=function(){
window.scrollTo(0, a_contents[5].offsetTop)
}
//获取页面上，导航条到顶部的位置
var a_navigation_bar = []
if(document.getElementsByClassName){//Chrome, FF
a_navigation_bar = document.getElementsByClassName("navigation")
} else {//IE
a_navigation_bar = my_getElementsByClassName("navigation")
}
//获取offsetTop
naviga_offsetTop = a_navigation_bar[0].offsetTop
a_navigation_bar[0].style.left = naviga_offsetLeft + "px"
//给滚动条以及鼠标加上滚动事件
if( window.attachEvent) //IE
{
window.attachEvent("onmousewheel", naviga_stay_top)
window.attachEvent("onscroll", naviga_stay_top)
document.attachEvent("onmousewheel", naviga_stay_top)
document.attachEvent("onscroll", naviga_stay_top)
} else {//Chrome ,FF
window.addEventListener("mousewheel", naviga_stay_top,false)
window.addEventListener("scroll", naviga_stay_top,false)
document.addEventListener("mousewheel", naviga_stay_top,false)
document.addEventListener("scroll", naviga_stay_top,false)
}
}
一般来讲实现导航栏指定是采用绝对定位的方式。示例代码如下：<div class="nav">这里是导航所在的DIV容器。</div>
CSS代码：
.nav{
position:fixed/* 绝对定位，fixed是相对于浏览器窗口定位。 */
top:0/* 距离窗口顶部距离 */
left:0/* 距离窗口左边的距离 */
width:100%/* 宽度设置为100% */
height:40px/* 高度 */
z-index:99/* 层叠顺序，数值越大就越高。页面滚动的时候就不会被其他内容所遮挡。 */
}
设置方式，原理及大致内容请看css代码注释
