js控制导航滚动

通过js获取视口高度，当超过高度时改变position的值为fixed，html在相应标签加入id= "float"

/**
 * Created by 刘吴江 on 2018/5/1.
 */
window.onload=
    function(){
        var oDiv = document.getElementById("float"),
            H = 0,
            Y = oDiv
        while (Y) {H += Y.offsetTop; Y = Y.offsetParent}
        window.onscroll = function()
        {
            var s = document.body.scrollTop || document.documentElement.scrollTop
            if(s>H) {
                oDiv.style = "position:fixed;top:0;"
            } else {
                oDiv.style = ""
            }
        }
    }