link a js file to an html file code example
Example 1: how to link your js file to html
<script src="index.js"></script>
Example 2: link javascript file to html
<script type="text/javascript" src="path-to-javascript-file.js"></script>
<script src="index.js"></script>
<script type="text/javascript" src="path-to-javascript-file.js"></script>