I\'m looking for simple code that adds a popup in my Google Apps Script Ui that comes up when I hit a submit button. The popup box would display a message and have a button
Since UiApp is depreciated, HTMLService should be used to create custom user interfaces.
To prompt simple popup to display a message, use alert
method of Ui class
var ui = DocumentApp.getUi();
ui.alert('Hello world');
will prompt simple popup with hello world and an ok button.
To display customized html template in Dialog, use HTMLService to create template and then pass it to showModalDialog
method of Ui Class
var html = HtmlService.createHtmlOutput("Hello world").setSandboxMode(HtmlService.SandboxMode.IFRAME);
DocumentApp.getUi().showModalDialog(html, "My Dialog");
HtmlService.createHtmlOutputFromFile
allows you to display html that is in a separate file. see the documentation