JS: BigInt tutorial

By Xah Lee. Date: 2026-04-22. Last updated: 2026-08-14.

What is big int

new in JS: ECMAScript 2020

BigInt is a primitive type . It lets you work with integers of arbitrary precision.

The Number type in JavaScript cannot represent integers bigger than Number.MAX_SAFE_INTEGER .

// problem of large integer in JavaScript

console.log(
 9007199254740993 ===
  9007199254740992,
);
// true

console.log(Number.MAX_SAFE_INTEGER);
// 9007199254740991

console.log(Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2);
// true

BigInt solves this by supporting integers with unlimited size (only limited by available memory).

Big int type

console.assert(typeof 123n === "bigint");

JS: Value Types

Create big int

Literal syntax

// put n at the end of digit sequence, makes it a big int type

// this is big int
console.log(3n);
// 3n

console.log(3n == 3);
// true

// very big number
console.log(1093508046768863039966381565n);
// 1093508046768863039966381565n

big int constructor

JS: bigint constructor

Basic arithmetic

BigInt supports the usual arithmetic operators.

// plus, add
console.log(3n + 2n)
// 5n

// minus, substraction
console.log(3n - 2n)
// 1n

// negation
console.log(-(-3n));
// 3n

console.log(-3n);
// -3n

// multiply
console.log(3n * 2n)
// 6n

// divide
console.log(10n / 2n);
// 5n

// not divisible. return integer quotient
console.log(11n / 5n);
// 2n

console.log(-11n / 5n);
// -2n

// mod, remainder
console.log(5n % 2n);
// 1n

// power
console.log(3n ** 2n);
// 9n

JS: Arithmetic Operators

🛑 WARNING: you cannot mix BigInt with Number type.

console.log(3n + 2);

// error: Uncaught (in promise) TypeError: Cannot mix BigInt and other types, use explicit conversions

Number comparison

console.log(3n < 4n);
// true

console.log(3n <= 3n);
// true

// s------------------------------

console.log(3n > 4n);
// false

console.log(3n >= 3n);
// true

// s------------------------------
// double equal

console.log(3n == 3n);
// true

console.log(3n != 3n);
// false

// s------------------------------
// triple equal

console.log(3n === 3n);
// true

console.log(3n !== 3n);
// false

JS: Number Comparison Operators

mix big int with normal number

console.log(3n < 4);
// true

console.log(3n <= 3);
// true

// s------------------------------

console.log(3n > 4);
// false

console.log(3n >= 3);
// true

// s------------------------------
// double equal

console.log(3n == 3);
// true

console.log(3n != 3);
// false

// s------------------------------

// WARNING. triple equal cannot be used.

console.log(3n === 3);
// false

console.log(3n !== 3);
// true

Convert to string, hexadecimal, format

// to string
console.log((12345678901234567890n).toString());
// "12345678901234567890"

// to hexadecimal
console.log((12345678901234567890n).toString(16));
// ab54a98ceb1f0ad2

// format
console.log((12345678901234567890n).toLocaleString());
// "12,345,678,901,234,567,890"

Converting between number and bigint

// bigint to num
// lossy if too big
console.log(Number(123n));
// 123

// num to bigint
console.log(BigInt(123));
// 123n

Convert to number

BigInt.asIntN
BigInt.asUintN

JS: BigInt .asIntN .asUintN

JSON does not support bigint

// Custom replacer / reviver
JSON.stringify({ big: 12345678901234567890n }, (k, v) =>
  typeof v === 'bigint' ? v.toString() + 'n' : v);

JSON.parse(json, (k, v) =>
  typeof v === 'string' && v.endsWith('n') ? BigInt(v.slice(0, -1)) : v);