客户端异步请求抛出的500友好错误信息，处理起来很困难，需要把后端代码逐个检查下。
若是抛出500错误详细信息，就可以快速把问题处理掉。
如果是响应的是文本，就用 response.text() 方法，JSON 就用 response.json() 方法。
async function bigFileUpload_click(sef) {const chunk_size = 1024*1024; // 1MB per chunkconst file = sef.files[0];const fileSize = file.size;const totalChunks = Math.ceil(fileSize/chunk_size); // 向上取整const progressBar = $$('#progressBar');console.log( file.name );return;for (let chunkIndex = 0; chunkIndex < totalChunks; chunkIndex++) {const start = chunkIndex * chunk_size;const end = Math.min(fileSize, start+chunk_size);const chunk = file.slice(start, end);const formData = new FormData();formData.append('act', 'bigFileUpload_click');formData.append('file', chunk);formData.append('fileName', file.name);formData.append('chunkIndex', chunkIndex);formData.append('totalChunks', totalChunks);progressBar.innerHTML = Math.ceil(chunkIndex/fileSize*100);await fetch(location.pathname,{method: 'POST',body: formData}).then(response => {if (response.status !== 200) {console.log('response:', response, response.text());}}).catch(error => {console.error('Error:', error)});;}progressBar.innerHTML = '100%';
}
