How. NET passes the value of a variable to the foreground JS in the background

How does the C # background computed value be assigned to the foreground

First defined in the background, example: public int ID, (to protected void Page_Load (object sender, EventArgs e),
You can then start the value in protected void Page_Load (object sender, EventArgs e) or get the value of the foreground input
Finally in the foreground JS var id= "<%=id%>";

2. This is the value of the pass variable name.
4. In HTML JS
6. var srcurl = <%=getUrl%>;
8. var srcurl = <%=getUrl%>;
10. In the CS class file
12. Public static string getUrl = "url";
14. Public static string getUrl = URL;
18. If you want to pass the value of a method
20. In HTML JS
22. var srcurl = <%=geturl ()%>;
24. var srcurl = <%=geturl ()%>;
26. C # code public static string GetUrl ()
28. { return "returned value"; }    
30. Public static string GetUrl () {return value;}

How. NET passes the value of a variable to the foreground JS in the background