Apps Script UI

Menus

onOpen() runs automatically when the file opens and builds the menu:

function onOpen(): void {
  SpreadsheetApp.getUi()
    .createMenu("My Add-on")
    .addItem("Do Something", "doSomething")
    .addSeparator()
    .addSubMenu(SpreadsheetApp.getUi().createMenu("More").addItem("Option A", "optionA"))
    .addToUi();
}

Menu item callbacks are referenced by function name as a string, not a reference — the function must be public (see Gotchas) and take no arguments.