import script html

HTML
<html>
  <head>
    <script type="text/javascript" src="/path/to/script.js"></script>
    ...<script src="PathToYourFile.js"> </script><script src="index.js"></script>  
    <script src="myscripts.js"></script>
  
 <script src="Your-JavaScript-File.js"></script> <!--If JS file is in same folder with HTML file-->
Source

Also in HTML: