Intersect() function for Google Apps Script

Intersect.gs

/**
 * Returns the intersection of two ranges, or null if there is no overlap.
 * @param {range} r1 Range 1
 * @param {range} r2 Range 2
*/
function Intersect(r1, r2) {
  if (r1.getSheet().getSheetId() !== r2.getSheet().getSheetId()) return null;

  const FIRSTROW = Math.max(r1.getRow(), r2.getRow());
  const LASTROW = Math.min(r1.getLastRow(), r2.getLastRow());
  const FIRSTCOL = Math.max(r1.getColumn(), r2.getColumn());
  const LASTCOL = Math.min(r1.getLastColumn(), r2.getLastColumn());

  if (FIRSTROW > LASTROW || FIRSTCOL > LASTCOL) return null;
  return r1.getSheet().getRange(FIRSTROW, FIRSTCOL, LASTROW - FIRSTROW + 1, LASTCOL - FIRSTCOL + 1);
}