include index.js in index.html code example
Example 1: html bind js file
<script type="text/javascript" src="path-to-javascript-file.js"></script>
Example 2: How to add js file to a site through url
var jsFile = document.createElement("script");
jsFile.src = "homePage.js"; // it can be path also "{themes('/scripts/homePage.js')}"
document.body.appendChild(jsFile); //append it as src to body