ASP. NET web pages (. aspx) Add User Controls (. ascx) without display issues

You can click the view to display the user control. However, when you add the control to a web form, it is shown as follows:

Run F5 and check the source code: code is available, but the page is blank.
Analyze the code and compare other web pages and code that can display the user control. It is found that only the following code is different: <script language = "JavaScript" src = ".. /.. /JS/test. JS "/>

Replace with: <script language = "JavaScript" src = ".../../JS/test. js"> </SCRIPT>

The problem is solved, and no problem is displayed during running !!

I hope that the experts will explain it below. I don't know whether the compiler has a problem or what is going on. I tried this many times (including re-compiling the project and aspnet_regiis-I.