how to call javascript function external file code example

Example 1: 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

Example 2: javascript class in external file

class User {
    //...
}

module.exports = User