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