根据我的经验，有两种方法可以解决这个问题:

Set a short-lived cookie on the download, and have JavaScript continually check for its existence. Only real issue is getting the cookie lifetime right - too short and the JavaScript can miss it, too long and it might cancel the download screens for other downloads. Using JavaScript to remove the cookie upon discovery usually fixes this. Download the file using fetch/XHR. Not only do you know exactly when the file download finishes, if you use XHR you can use progress events to show a progress bar! Save the resulting blob with msSaveBlob in Internet Explorer or Edge and a download link (like this one) in Firefox and Chrome. The problem with this method is that iOS Safari doesn't seem to handle downloading blobs right - you can convert the blob into a data URL with a FileReader and open that in a new window, but that's opening the file, not saving it.

如果您下载了一个文件，该文件是保存的，而不是在文档中，则无法确定下载何时完成，因为它不在当前文档的范围内，而是浏览器中的一个单独进程。

如果XMLHttpRequest和一个blob不是一个选项，那么你可以在一个新窗口中打开你的文件，并检查是否有任何元素被填充到该窗口体中。

var form = document.getElementById("frmDownlaod"); form.setAttribute("action", "downoad/url"); form.setAttribute("target", "downlaod"); var exportwindow = window.open("", "downlaod", "width=800,height=600,resizable=yes"); form.submit(); var responseInterval = setInterval(function() { var winBody = exportwindow.document.body if(winBody.hasChildNodes()) // Or 'downoad/url' === exportwindow.document.location.href { clearInterval(responseInterval); // Do your work. // If there is an error page configured in your application // for failed requests, check for those DOM elements. } }, 1000) // Better if you specify the maximum number of intervals

问题是在生成文件时有一个“等待”指示器，然后在文件下载后恢复正常。我喜欢这样做的方式是使用一个隐藏的iFrame和钩子帧的onload事件，让我的页面知道什么时候开始下载。

但是onload不会在Internet Explorer中触发文件下载(就像使用附件头令牌一样)。轮询服务器是可行的，但我不喜欢这种额外的复杂性。这就是我所做的:

目标隐藏iFrame像往常一样。 生成内容。用 2分钟内绝对超时。 发送JavaScript重定向回 调用客户端，本质上调用 第二次生成页面。注意:这将导致在Internet Explorer中触发onload事件，因为它就像一个普通页面一样。 从缓存中删除内容并 发送给客户端。

免责声明:不要在繁忙的站点上这样做，因为缓存会增加。但实际上，如果您的站点非常繁忙，那么长时间运行的进程无论如何都会耗尽您的线程。

下面是隐藏代码的样子，这是您真正需要的。

public partial class Download : System.Web.UI.Page
{
    protected System.Web.UI.HtmlControls.HtmlControl Body;

    protected void Page_Load( object sender, EventArgs e )
    {
        byte[ ] data;
        string reportKey = Session.SessionID + "_Report";

        // Check is this page request to generate the content
        //    or return the content (data query string defined)
        if ( Request.QueryString[ "data" ] != null )
        {
            // Get the data and remove the cache
            data = Cache[ reportKey ] as byte[ ];
            Cache.Remove( reportKey );

            if ( data == null )
                // send the user some information
                Response.Write( "Javascript to tell user there was a problem." );
            else
            {
                Response.CacheControl = "no-cache";
                Response.AppendHeader( "Pragma", "no-cache" );
                Response.Buffer = true;

                Response.AppendHeader( "content-disposition", "attachment; filename=Report.pdf" );
                Response.AppendHeader( "content-size", data.Length.ToString( ) );
                Response.BinaryWrite( data );
            }
            Response.End();
        }
        else
        {
            // Generate the data here. I am loading a file just for an example
            using ( System.IO.FileStream stream = new System.IO.FileStream( @"C:\1.pdf", System.IO.FileMode.Open ) )
                using ( System.IO.BinaryReader reader = new System.IO.BinaryReader( stream ) )
                {
                    data = new byte[ reader.BaseStream.Length ];
                    reader.Read( data, 0, data.Length );
                }

            // Store the content for retrieval
            Cache.Insert( reportKey, data, null, DateTime.Now.AddMinutes( 5 ), TimeSpan.Zero );

            // This is the key bit that tells the frame to reload this page
            //   and start downloading the content. NOTE: Url has a query string
            //   value, so that the content isn't generated again.
            Body.Attributes.Add("onload", "window.location = 'binary.aspx?data=t'");
        }
    }

来自其他地方的有效解决方案:

/**
 *  download file, show modal
 *
 * @param uri link
 * @param name file name
 */
function downloadURI(uri, name) {
// <------------------------------------------       Do something (show loading)
    fetch(uri)
        .then(resp => resp.blob())
        .then(blob => {
            const url = window.URL.createObjectURL(blob);
            const a = document.createElement('a');
            a.style.display = 'none';
            a.href = url;
            // the filename you want
            a.download = name;
            document.body.appendChild(a);
            a.click();
            window.URL.revokeObjectURL(url);
            // <----------------------------------------  Detect here (hide loading)
            alert('File detected');
        })
        .catch(() => alert('An error sorry'));
}

你可以使用它:

downloadURI("www.linkToFile.com", "file.name");

一个非常简单(蹩脚)的一行解决方案是使用window.onblur()事件关闭加载对话框。当然，如果它花了太长时间，用户决定做其他事情(如阅读电子邮件)，加载对话框将关闭。