在客户端Javascript方法之后运行服务器方法

Is it possible to setup an asp button so that when it is clicked, the client-side javascript will run, and then the server-side c# method will run, but only after the prior javascript has completed? The goal being when the client submits a form, the 3rd-party jscript does its thing and sends out the form data. When that is done, the server-side method will run, create the file it needs to, and then post it back so that the client can download it. I have both of these working separately, but trying to put them together has been the issue. Is it possible to setup an asp button so that w