So I have a script being run when a user clicks on a button in sheets. The button is linked to a script. I want a the loading message popped up so they know the script is still running and not edit anything in the tab.

I have tried several scripts I could find online but its not working as intended.

This is what I have tried but its not doing antyhing.

function showDialog() {

var ui = SpreadsheetApp.getUi();
// Display a modal dialog box with custom HtmlService content.
var htmlOutput = HtmlService
.setWidth(250)
.setHeight(300);
ui.showModalDialog(htmlOutput, 'Script Running');

}

So basically what I just want is

1. Button is clicked, script runs
2. while script is running, Loading message will appear somewhere in the sheet
3. Script is finished, Loading message disappears. No additional message pops up.