link js file to index.html

<script src="Your-JavaScript-File.js"></script> <!--If JS file is in same folder with HTML file-->

 <script src="your js file"></script>

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