页面滚动时头部显示效果实现

//jq ¹ö¶¯
$(document).ready(function(){
    $(window).scroll(function(){
      if($(window).scrollTop()>80){
        $('.header').addClass('position-f');
        $('#replaceImg').attr('src','../imgs/ywlogo .png');
        $('.nav2').css('display','none');
      }else{
          $('.header').removeClass('position-f');
          $('#replaceImg').attr('src','../imgs/logo.png');
          $('.nav2').css('display','block');
      }
    })
   })

//js¹ö¶¯¸ß
var head6  = document.getElementById("travel-header");
var search6  = document.getElementById("travel-search");
var banner6  = document.getElementById("travel-banner");
var title6  = document.getElementById("travel-title");
var nav6  = document.getElementById("travel-nav");
var box6  = document.getElementsByClassName("travel-box")[0];

var nav62  = document.getElementById("travel-nav2");
var nav62Height = head6.offsetHeight+search6.offsetHeight+banner6.offsetHeight+title6.offsetHeight+nav6.offsetHeight+box6.offsetHeight;
var headeHeight1 = head6.offsetHeight;
window.onscroll = function(){
    var _top = document.body.scrollTop || document.documentElement.scrollTop;
    if(_top>headeHeight1){
        head6.style.position="fixed";