html怎么实现进度条

下载进度：<progress value="22" max="100"></progress>

<progress id=&#39;progress1&#39; value="0" max="100"></progress><button onclick="start_run(100)">下载</button><script>function start_run(n){    if(n==0){alert("下载完成")}    var progress1=document.getElementById("progress1")    n=n-1    cur_task=100-n    progress1.value=cur_task    setTimeout("start_run("+n+")",100)    }</script>