let bar;
    let scrollTop = 0;
    window.onload = function() {
        bar = document.getElementsByClassName("bar")[0];
            
        window.addEventListener("scroll",function(e){
            scrollTop = document.documentElement.scrollTop;
            let per = Math.round(scrollTop / (document.body.scrollHeight - window.innerHeight) * 100);
            console.log(window.innerHeight);
            //console.log(bar)
            bar.style.height = per + "%";
        }, false)
    }