title: How can I tell whether a JavaScript file has already been included in an ASP.NET page?
body: <p>I have an ASP.NET user control (.ascx file). In this user control I want to use a .js file.</p>
  
  <p>So I include <code>&lt;script src="file.js" type"text/javascript"&gt;&lt;/script&gt;</code> on the page.</p>
  
  <p>However, sometimes I use this user control in a webpage where this same script has already been loaded.</p>
  
  <p>How can I add a <code>&lt;script /&gt;</code> declaration that will render on the page only if the page doesn't already contain another <code>&lt;script /&gt;</code> tag for the same script?</p>