JS formData到服务器的ajax分块上传，所有的分块都上传完毕JS完整代码和 VB WebMethod 后端完整代码

在JavaScript中，你可以使用`FormData`配合`XMLHttpRequest`或`fetch` API来进行分块上传。这里提供一个基本的示例，假设我们有10MB的数据，分成100个小块，每块10KB：

**前端（JavaScript）代码：**

var xhr = new XMLHttpRequest();
xhr.open('POST', '/api/upload', true);
xhr.upload.onprogress = function(event) {
  if (event.lengthComputable) {
    var percentComplete = Math.round((event.loaded / event.total) * 100);
    console.log(`已上传 ${percentComplete}%`);
  }
};

const blockSize = 10 * 1024; // 单位字节
const data = ... // 你的原始数据
let index = 0;
function uploadChunk() {
  if (index < data.length / blockSize) {
    const chunkData = data.slice(index * blockSize, (index + 1) * blockSize);
    xhr.setRequestHeader('Content-Type', 'multipart/form-data');
    xhr.send(new Blob([chunkData], {type: 'application/octet-stream'}));
    index++;
    setTimeout(uploadChunk, blockSize); // 每次上传完一块等待一段时间再继续
  } else {
    xhr.onload = function() {
      console.log("所有块上传完成");
    };
  }
}
uploadChunk(); // 开始上传

**后端（VB .NET 和 ASP.NET AJAX 示例，假设WebMethod名为`UploadChunks`）：**

Imports System.IO

<WebMethod()>
Public Async Function UploadChunks(filePart As Byte()) As String
    Dim fileLength As Integer = filePart.Length
    Dim totalUploaded As Integer = 0
    
    While totalUploaded < fileLength
        Dim received As Integer = Await ProcessNextChunk(filePart, totalUploaded)
        If received > 0 Then
            totalUploaded += received
            Console.WriteLine($"已接收 {totalUploaded} 字节")
        Else
            Exit While
        End If
    End While

    Return "所有块成功接收"
End Function

Async Function ProcessNextChunk(buffer As Byte(), uploadedSoFar As Integer) As Task(Of Integer)
    ' 这里处理每个接收到的文件块，将其保存到数据库、文件等，然后返回剩余需要接收的字节数
    ' ... (实际处理逻辑)
    ' 返回剩余字节数，例如返回buffer.Length - uploadedSoFar 或者 0 如果已完成处理
    ' 返回值取决于实际操作
End Function

请注意，这只是一个基础示例，实际应用中可能需要额外的安全措施和错误处理。