console 命令行工具 X clear

console

var down = 0
function start() {
  if (down === 0) {
    down = 1
    var progress = 0
    var timer = setInterval(function() {
      progress ++
	    document.getElementById('progress').value = progress
      if (progress >= 100) {
        clearInterval(timer)
        down = 0
      }
    }, 100)
  } else {
    alert('正在下载中')
  }
}

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <title>Document</title>
</head>
<body>
  <div id="container">
    <progress id="progress" value="0" max="100"></progress>
    <button onclick="start()">下载</button>
  </div>
</body>
</html>

#container {
  display: flex;
  justify-content: center;
  align-items: center;
}
button {
  background-color: transparent;
  border: 1px solid #DDDDDD;
  margin: 10px;
}
botton:hover {
  cursor: pointer;
}