Creating a javascript file to use in other places

javascript_app.js

// More details: https://addyosmani.com/resources/essentialjsdesignpatterns/book/#revealingmodulepatternjavascript
// https://stackoverflow.com/a/7513721
var JsApp = (function() {

    function callback() {
        alert("done");
    };

    return {
        callbackAlert: callback
    };

})();

// Usage: 
JsApp.callbackAlert();