AJAX和FETCH请求进度条

要实现一个AJAX和FETCH请求的进度条，你可以在发送请求前设置一个监听器来跟踪加载的进度。以下是使用AJAX和FETCH分别实现进度条的简单示例。

AJAX 示例:

function updateProgress(event) {
  if (event.lengthComputable) {
    var percentComplete = (event.loaded / event.total) * 100;
    console.log(percentComplete.toFixed(2) + '%');
    // 更新进度条的逻辑
  }
}
 
var xhr = new XMLHttpRequest();
xhr.open('GET', 'your-file-url', true);
xhr.onprogress = updateProgress;
xhr.send();

FETCH 示例:

fetch('your-file-url', {
  method: 'GET',
  // 如果你想要获取进度更新，需要指定 `body: new ProgressEvent()`
  body: new ProgressEvent()
}).then(response => {
  const contentLength = response.headers.get('Content-Length');
  return response.body.getReader({ mode: 'byob' }).then(reader => {
    let received = 0;
    const reader = response.body.getReader();
    const total = contentLength ? Number(contentLength) : null;
    return streamBlobFromReader(reader, total, (chunk) => {
      received += chunk.byteLength;
      console.log((received / total * 100).toFixed(2) + '%');
      // 更新进度条的逻辑
    });
  });
});
 
function streamBlobFromReader(reader, total, onProgress) {
  const contentType = response.headers.get('Content-Type');
  const blob = new Blob([], { type: contentType });
  const writer = new BlobWriter(blob);
 
  return reader.enqueue().then(() => {
    return writer.getBlob();
  });
}
 
class BlobWriter {
  constructor(blob) {
    this._blob = blob;
    this._writer = new BlobWriter.Writer(blob);
  }
 
  getBlob() {
    return this._writer.getBlob();
  }
 
  enqueue(chunk) {
    return this._writer.write(chunk).then(() => {
      // 更新进度条的逻辑
    });
  }
}

注意：以上代码示例中的 // 更新进度条的逻辑 需要替换为你的实际更新进度条的逻辑。AJAX 示例中的 updateProgress 函数会在事件发生时被调用，并且你可以在该函数中更新进度条。FETCH 示例中，你需要使用实际的DOM操作来更新进度条。