使用fetch方法如何去跟踪下载进度？"```javascript const url = 'https://exam

"```javascript const url = 'example.com/file.zip';

fetch(url).then(response => { const total = response.headers.get('content-length'); let downloaded = 0;

const reader = response.body.getReader();

reader.read().then(function processResult(result) {
    if (result.done) {
        console.log('Download complete');
        return;
    }

    const chunk = result.value;
    downloaded += chunk.byteLength;

    // 计算下载进度
    const progress = Math.round((downloaded / total) * 100);
    console.log(`Downloaded ${progress}%`);

    // 继续读取下一个数据块
    return reader.read().then(processResult);
});

}).catch(error => { console.error('Download error:', error); });