BigInt

JavaScript · Reference cheat sheet

📋 Overview

BigInt represents arbitrary-precision integers. Use when values exceed Number.MAX_SAFE_INTEGER (±2⁵³−1), such as IDs, cryptography sizes, or exact integer math. BigInts cannot mix with Numbers in arithmetic without explicit conversion.

🔧 Core concepts

• Literals: 10n, -1n.
• Construct: BigInt(10), BigInt("9007199254740993").
• Ops: + - * / % ** and bitwise on BigInts only (/ truncates toward zero).
• Compare: < > <= >= work with Numbers; === does not coerce.
• Typed arrays: BigInt64Array, BigUint64Array.
• No Math.*: use explicit BigInt helpers.

const huge = 9007199254740993n;
huge + 1n; // 9007199254740994n

💡 Examples

Number.MAX_SAFE_INTEGER; // 9007199254740991
9007199254740993; // loses precision as Number
9007199254740993n; // exact

// Conversion
BigInt(42); // 42n
Number(42n); // 42 — may lose precision for large values
42n === 42; // false
42n == 42; // true (avoid ==)

// Arithmetic
(2n ** 10n); // 1024n
10n / 3n; // 3n (truncates)

// Mixing requires cast
const n = 5;
// 5n + n; // TypeError
5n + BigInt(n); // 10n

// Comparisons
1n < 2; // true
0n === 0; // false

// JSON — not supported natively
JSON.stringify({ id: 1n }); // throws
// serialize as string:
JSON.stringify({ id: 1n.toString() });

// Typed array
const buf = new BigInt64Array([1n, -2n]);

function fib(n) {
  let a = 0n,
    b = 1n;
  for (let i = 0; i < n; i++) [a, b] = [b, a + b];
  return a;
}

⚠️ Pitfalls

• Mixing BigInt and Number in +/* throws TypeError.
• Math.max(1n, 2n) throws — no Math support.
• Division truncates; there is no BigInt float.
• JSON.stringify cannot serialize BigInt — convert to string/number carefully.
• Unary +bigint is invalid; use Number(bigint) or comparisons.

🔗 Related

• number.md — IEEE floats & safe integers
• typed_arrays.md — BigInt64Array
• json.md — serialization
• equality.md — == vs ===
• type_coercion.md — conversions