Inserts an RFC2822 Timestamp at the cursor location of a Google Document

insertTime.gs

// https://developers.google.com/apps-script/reference/document
function insertTimeStampAtCursor() {
  
  const doc = DocumentApp.getActiveDocument();
  const selection = doc.getSelection();
  const cursor = doc.getCursor();
  const dateTimeString = rfc2822Datetime();
  
  if (selection) {
    const selectedElements = selection.getRangeElements();
    
    // might break if it's not text
    selectedElements[0]
    .getElement()
    .asText()
    .setText(dateTimeString)
    .setFontFamily("Roboto Mono");
    
    for (var i = 1; i < selectedElements.length; i++) {
      const selectedElement = selectedElements[i];
      const element = selectedElement.getElement();
      if (selectedElement.isPartial()) {
        element
        .asText()
        .deleteText(
          selectedElement.getStartOffset(), 
          selectedElement.getEndOffsetInclusive()
        );
      } else {
        element.removeFromParent();
      }
    }
    
  } else if (cursor) {
    
    const element = cursor.insertText(dateTimeString);
    
    if (element) {
      element.setFontFamily("Roboto Mono");
    } else {
      DocumentApp.getUi().alert("Cannot insert text at this cursor location.");
    }
    
  } else {
    DocumentApp.getUi().alert("Cannot find a cursor or selection in the document.");
  }
  
}

function rfc2822Datetime() {
  const now = new Date();
  const timeZone = Session.getScriptTimeZone();
  const rfc2822Format = "EEE, dd MMM yyyy HH:mm:ss Z";
  const dateTimeString = Utilities.formatDate(now, timeZone, rfc2822Format);
  return dateTimeString;
}

function menu() {
  DocumentApp.getUi().createMenu("Utils")
  .addItem("Insert timestamp", "insertTimeStampAtCursor")
  .addToUi();
}

function onOpen() {
  menu();
}