function onOpen(e) {
  const prop = PropertiesService.getScriptProperties();
  const sheetName = e.range.getSheet().getSheetName();
  prop.setProperty("previousSheet", sheetName);
}

function onSelectionChange(e) {
  const prop = PropertiesService.getScriptProperties();
  const previousSheet = prop.getProperty("previousSheet");
  const range = e.range;
  const a1Notation = range.getA1Notation();
  const sheetName = range.getSheet().getSheetName();
  if (sheetName != previousSheet) {
    range.setValue(`Changed tab from ${previousSheet} to ${sheetName}. ${a1Notation}`);

    // When the tab is changed, this script is run.

  } else {
    range.setValue(a1Notation);
  }
  prop.setProperty("previousSheet", sheetName);
}