JS分块上传 服务器会暂存块，直到所有的块都上传完毕JS完整代码和 VB Implements IHttpHandler后端完整代码

在JavaScript中实现文件分块上传，通常使用的是FileReader API配合Ajax请求。以下是简化版的前端代码示例：

// 假设我们有最大块大小限制和URL
const chunkSize = 1048576; // 1MB
const url = '/upload';

function uploadChunk(file, part) {
  const reader = new FileReader();
  reader.onload = function (event) {
    const xhr = new XMLHttpRequest();
    xhr.open('PUT', `${url}?part=${part}`);
    xhr.setRequestHeader('Content-Type', 'application/octet-stream');
    xhr.send(event.target.result);
    xhr.onloadend = function () {
      if (xhr.status === 200) {
        console.log(`Uploaded block ${part}`);
      } else {
        console.error('Error uploading block:', xhr.statusText);
      }
    };
  };
  reader.readAsArrayBuffer(file.slice(part * chunkSize, (part + 1) * chunkSize));
}

// 开始上传
uploadChunk(file, 0);

对于VB.NET实现IHttpHandler的后端，由于涉及到服务器端技术和框架，这里给出一个简单的概念代码，假设你使用ASP.NET MVC或Web API:

Imports System.IO
Imports Microsoft.AspNetCore.Mvc
Imports Microsoft.AspNetCore.Http

Public Class FileUploadHandler : Inherits IHttpActionResult
    Private _chunkIndex As Integer
    Private _file As HttpPostedFileBase
    Private _totalChunks As Integer
    Private _chunkSize As Integer
    Private _baseUrl As String

    Public Sub New(file As HttpPostedFileBase, chunkIndex As Integer, totalChunks As Integer, chunkSize As Integer, baseUrl As String)
        Me._file = file
        Me._chunkIndex = chunkIndex
        Me._totalChunks = totalChunks
        Me._chunkSize = chunkSize
        Me._baseUrl = baseUrl
    End Sub

    Public Async Function ExecuteResultAsync() As Task(Of Object)
        Dim buffer = New ArraySegment(Of Byte>(_file.InputStream.ReadBlock(_chunkSize))
        Using client = New HttpClient()
            Await client.PutAsync($"{_baseUrl}?part={_chunkIndex}", New ByteArrayContent(buffer))
        End Using

        If _chunkIndex < _totalChunks - 1 Then
            Return CreatedAtAction("HandleNextChunk", New With {.chunkIndex = _chunkIndex + 1})
        Else
            ' 所有块已上传，处理完成逻辑
            ' ...
            Return Ok()
        End If
    End Function

    Private Async Function HandleNextChunk(chunkIndex As Integer) As Task(Of IHttpActionResult)
        ' 调用这个Action处理下一个块
        ' ...
    End Function
End Class

请注意，这只是一个简化的例子，实际生产环境中需要添加错误处理、断点续传等功能，并确保服务器端的安全性。