首先，这里有一篇文章：

使用ASP.NET Web API中的jQuery AJAX进行文件上载 [ ^ ]



现在为了支持不太现代的浏览器，您可能希望在HTML4浏览器中包含支持文件上传的库，或者使用iframe。

First, there's an article here:
File Upload using jQuery AJAX in ASP.NET Web API[^]

Now for backward support for less-modern browsers you'll likely want to include a library that supports file upload on HTML4- browsers, or use an iframe.