MDN doc

BigInt is a built-in object that provides a way to represent whole
numbers larger than 2^53 - 1, which is the largest number JavaScript
can reliably represent with the Number primitive and represented by
the Number.MAX_SAFE_INTEGER constant. BigInt can be used for
arbitrarily large integers.

Difference:

• BigInt cannot be used with methods in the built-in Math object and cannot be mixed with instances of Number in operations


• Because coercing between Number and BigInt can lead to loss of
  precision, it is recommended to only use BigInt when values greater
  than 2^53 are reasonably expected and not to coerce between the two
  types.