js怎么判断有没有下载文件

function downloadFile(url) {
    return new Promise((resolve, reject) => {
        const xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'blob';
        xhr.onload = function() {
            if (xhr.status === 200) {
                resolve(xhr.response);
            } else {
                reject(new Error(`Failed to download file: ${xhr.statusText}`));
            }
        };
        xhr.onerror = function() {
            reject(new Error('Network error'));
        };
        xhr.send();
    });
}

downloadFile('https://example.com/file.pdf')
    .then(blob => {
        console.log('File downloaded successfully');
        // 处理下载的文件
    })
    .catch(error => {
        console.error(error);
    });

async function downloadFile(url) {
    try {
        const response = await fetch(url);
        if (!response.ok) {
            throw new Error(`Failed to download file: ${response.statusText}`);
        }
        const blob = await response.blob();
        console.log('File downloaded successfully');
        // 处理下载的文件
        return blob;
    } catch (error) {
        console.error(error);
    }
}

downloadFile('https://example.com/file.pdf');

function triggerDownload(url, filename) {
    const link = document.createElement('a');
    link.href = url;
    link.download = filename;
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
    console.log('Download started');
}

triggerDownload('https://example.com/file.pdf', 'file.pdf');

if ('serviceWorker' in navigator) {
    window.addEventListener('load', () => {
        navigator.serviceWorker.register('/sw.js')
            .then(registration => {
                console.log('Service Worker registered with scope:', registration.scope);
            })
            .catch(error => {
                console.error('Service Worker registration failed:', error);
            });
    });
}

self.addEventListener('fetch', event => {
    if (event.request.url.endsWith('.pdf')) {
        event.respondWith(
            fetch(event.request)
                .then(response => {
                    if (!response.ok) {
                        throw new Error(`Failed to download file: ${response.statusText}`);
                    }
                    return response.blob();
                })
                .then(blob => {
                    console.log('File downloaded successfully');
                    // 处理下载的文件
                    return new Response(blob);
                })
                .catch(error => {
                    console.error(error);
                    return new Response('Error downloading file', { status: 500 });
                })
        );
    }
});