Q:

use .js file in C#

Sorry for such a basic question but i am not that used to JavaScript.
I have a JavaScript (DatePicker.js). I want to add a TextBox on emp_master.aspx that would call the .js function. 
But how do I use .js in C# i.e. where do I cal the .js file?

A:

Common practice is to include js and css files on master pages (files with .master extension).
Simplest example
<html>
  <head>
   <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
   <title>Тег LINK</title>  
   <link rel="stylesheet" type="text/css" href="styles.css">
   <script type="text/javascript" src="DatePicker.js"></script>
  </head> 
  <body>
    <p>...</p>
  </body>
</html>

