function onOpen(e) {
  // Builds a menu that displays under the Extensions menu in Sheets.
  let menu = SpreadsheetApp.getUi().createAddonMenu()

  menu
    .addItem('Delete blank rows (from selected rows only)', 'deleteEmptyRows')
    .addItem('Delete blank columns (from selected columns only)', 'deleteEmptyColumns')
    .addItem('Crop sheet to data range', 'cropSheet')
    .addSeparator()
    .addItem('Fill in blank rows below', 'fillDownData')
    .addSeparator()
    .addItem('About', 'aboutApp')
    .addToUi();
}
Creates a menu entry in the Google Sheets Extensions menu when the document is opened.

@param {object} e The event parameter for a simple onOpen trigger.