const a = 9007199254740991n; // MAX_SAFE_INTEGER as BigInt
const b = 2n;
const c = a + b;

const result = [
  a === 9007199254740991,
  a + 1n === 9007199254740992n,
  typeof c,
  c > Number.MAX_SAFE_INTEGER,
  BigInt(9007199254740992) - BigInt(9007199254740991)
];

console.log(result);