面是一种基于前端分片上传，后端合并的方法的代码实现：

前端代码（HTML + JavaScript）：

<input type="file" id="fileInput">
<button onclick="uploadFile()">Upload</button><script>
function uploadFile() {var fileInput = document.getElementById('fileInput');var file = fileInput.files[0];var chunkSize = 5 * 1024 * 1024; //每个分片大小为5MBvar totalChunks = Math.ceil(file.size / chunkSize); //总分片数var currentChunk = 0; //当前上传的分片序号var reader = new FileReader();reader.onload = function(e) {var xhr = new XMLHttpRequest();xhr.open('POST', '/upload', true);xhr.setRequestHeader('Content-Type', 'application/octet-stream');xhr.setRequestHeader('X-Chunk-Number', currentChunk);xhr.setRequestHeader('X-Total-Chunks', totalChunks);xhr.onload = function() {currentChunk++;if (currentChunk < totalChunks) {uploadChunk();} else {alert('File uploaded successfully!');}};xhr.send(e.target.result);};function uploadChunk() {var start = currentChunk * chunkSize;var end = Math.min(start + chunkSize, file.size);var chunk = file.slice(start, end);reader.readAsArrayBuffer(chunk);}uploadChunk();
}
</script>

后端代码（Node.js + Express）：

const express = require('express');
const app = express();
const fs = require('fs');app.use(express.json());app.post('/upload', (req, res) => {const chunkNumber = req.headers['x-chunk-number'];const totalChunks = req.headers['x-total-chunks'];const fileStream = fs.createWriteStream('uploaded_file', { flags: 'a' });req.pipe(fileStream);if (chunkNumber == totalChunks - 1) {fileStream.on('finish', () => {res.sendStatus(200);});}
});app.listen(3000, () => {console.log('Server started on port 3000');
});

前端使用了HTML的<input type="file">标签和JavaScript的FileReader对象来实现分片读取文件，并通过XMLHttpRequest发送每个分片到后端。

后端使用Node.js和Express框架，接收到每个分片后将其写入到文件中，当收到最后一个分片时，触发finish事件，表示文件上传完成。