BigInt - JavaScript | MDN

BigInt value
, also sometimes just called a
BigInt
, is a
bigint
primitive
, created by appending
to the end of an integer literal, or by calling the
BigInt()
function (without the
new
operator) and giving it an integer value or string value.
js
const previouslyMaxSafeInteger = 9007199254740991n;

const alsoHuge = BigInt(9007199254740991);
// 9007199254740991n

const hugeString = BigInt("9007199254740991");
// 9007199254740991n

const hugeHex = BigInt("0x1fffffffffffff");
// 9007199254740991n

const hugeOctal = BigInt("0o377777777777777777");
// 9007199254740991n

const hugeBin = BigInt(
"0b11111111111111111111111111111111111111111111111111111",
);
// 9007199254740991n
BigInt values are similar to Number values in some ways, but also differ in a few key matters: A BigInt value cannot be used with methods in the built-in
Math
object and cannot be mixed with a Number value in operations; they must be coerced to the same type. Be careful coercing values back and forth, however, as the precision of a BigInt value may be lost when it is coerced to a Number value.
When tested against
typeof
, a BigInt value (
bigint
primitive) will give
"bigint"
js
typeof 1n === "bigint"; // true
typeof BigInt("1") === "bigint"; // true
A BigInt value can also be wrapped in an
Object
js
typeof Object(1n) === "object"; // true
Most operators support BigInts, however most do not permit operands to be of mixed types — both operands must be BigInt or neither:
Arithmetic operators
**
Bitwise operators
>>
<<
Unary negation (
Increment/decrement
++
--
The boolean-returning operators allow mixing numbers and BigInts as operands:
A couple of operators do not support BigInt at all:
Special cases:
Addition (
) involving a string and a BigInt returns a string.
Division (
) truncates fractional components towards zero, since BigInt is unable to represent fractional quantities.
js
const previousMaxSafe = BigInt(Number.MAX_SAFE_INTEGER); // 9007199254740991n
const maxPlusOne = previousMaxSafe + 1n; // 9007199254740992n
const theFuture = previousMaxSafe + 2n; // 9007199254740993n, this works now!
const prod = previousMaxSafe * 2n; // 18014398509481982n
const diff = prod - 10n; // 18014398509481972n
const mod = prod % 10n; // 2n
const bigN = 2n ** 54n; // 18014398509481984n
bigN * -1n; // -18014398509481984n
const expected = 4n / 2n; // 2n
const truncated = 5n / 2n; // 2n, not 2.5n
A BigInt value is not strictly equal to a Number value, but it
is
loosely so:
js
0n === 0; // false
0n == 0; // true
A Number value and a BigInt value may be compared as usual:
js
1n < 2; // true
2n > 1; // true
2 > 2; // false
2n > 2; // false
2n >= 2; // true
BigInt values and Number values may be mixed in arrays and sorted:
js
const mixed = [4n, 6, -12n, 10, 4, 0, 0n];
// [4n, 6, -12n, 10, 4, 0, 0n]

mixed.sort(); // default sorting behavior
// [ -12n, 0, 0n, 10, 4n, 4, 6 ]

mixed.sort((a, b) => a - b);
// won't work since subtraction will not work with mixed types
// TypeError: can't convert BigInt value to Number value

// sort with an appropriate numeric comparator
mixed.sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
// [ -12n, 0, 0n, 4n, 4, 6, 10 ]
Note that comparisons with
Object
-wrapped BigInt values act as with other objects, only indicating equality when the same object instance is compared:
js
Object(0n) === 0n; // false
Object(0n) === Object(0n); // false

const o = Object(0n);
o === o; // true
Because coercing between Number values and BigInt values can lead to loss of precision, the following are recommended:
Only use a BigInt value when values greater than 2
53
are reasonably expected.
Don't coerce between BigInt values and Number values.
A BigInt value follows the same conversion rules as Numbers when:
Namely, only
0n
is
falsy
; everything else is
truthy
js
if (0n) {
console.log("Hello from the if!");
} else {
console.log("Hello from the else!");
// "Hello from the else!"

0n || 12n; // 12n
0n && 12n; // 0n
Boolean(0n); // false
Boolean(12n); // true
!12n; // false
!0n; // true
The operations supported on BigInt values are not constant-time and are thus open to
timing attacks
. JavaScript BigInts therefore could be dangerous for use in cryptography without mitigating factors. As a very generic example, an attacker could measure the time difference between
101n ** 65537n
and
17n ** 9999n
, and deduce the magnitude of secrets, such as private keys, based on the time elapsed. If you still have to use BigInts, take a look at the
Timing attack FAQ
for general advice regarding the issue.
Using
JSON.stringify()
with any BigInt value will raise a
TypeError
, as BigInt values aren't serialized in JSON by default. However,
JSON.stringify()
specifically leaves a backdoor for BigInt values: it would try to call the BigInt's
toJSON()
method. (It doesn't do so for any other primitive values.) Therefore, you can implement your own
toJSON()
method (which is one of the few cases where patching built-in objects is not explicitly discouraged):
js
BigInt.prototype.toJSON = function () {
return { $bigint: this.toString() };
};
Instead of throwing,
JSON.stringify()
now produces a string like this:
js
console.log(JSON.stringify({ a: 1n }));
// {"a":{"$bigint":"1"}}
If you do not wish to patch
BigInt.prototype
, you can use the
replacer
parameter of
JSON.stringify
to serialize BigInt values:
js
const replacer = (key, value) =>
typeof value === "bigint" ? { $bigint: value.toString() } : value;

const data = {
number: 1,
big: 18014398509481982n,
};
const stringified = JSON.stringify(data, replacer);

console.log(stringified);
// {"number":1,"big":{"$bigint":"18014398509481982"}}
You can then use the
reviver
parameter of
JSON.parse
to handle them:
js
const reviver = (key, value) =>
value !== null &&
typeof value === "object" &&
"$bigint" in value &&
typeof value.$bigint === "string"
? BigInt(value.$bigint)
: value;

const payload = '{"number":1,"big":{"$bigint":"18014398509481982"}}';
const parsed = JSON.parse(payload, reviver);

console.log(parsed);
// { number: 1, big: 18014398509481982n }
Note:
While it's possible to make the replacer of
JSON.stringify()
generic and properly serialize BigInt values for all objects as shown above, the reviver of
JSON.parse()
has to be used with caution, because the serialization is
irreversible
: it's not possible to distinguish between an object that happens to have a property called
$bigint
and an actual BigInt.
In addition, the example above creates an entire object during replacing and reviving, which may have performance or storage implications for larger objects containing many BigInts. If you know the shape of the payload, it may be better to just serialize them as strings and revive them based on the property key's name instead.
In fact, JSON allows number literals that are arbitrarily long; they just cannot be parsed to full precision in JavaScript. If you are communicating with another program in a language that supports longer integers (such as 64-bit integers), and you want to transmit the BigInt as a JSON number instead of a JSON string, see
Lossless number serialization
Many built-in operations that expect BigInts first coerce their arguments to BigInts.
The operation
can be summarized as follows:
BigInts are returned as-is.
undefined
and
null
throw a
TypeError
true
turns into
1n
false
turns into
0n
Strings are converted by parsing them as if they contain an integer literal. Any parsing failure results in a
SyntaxError
. The syntax is a subset of
string numeric literals
, where decimal points or exponent indicators are not allowed.
Numbers
throw a
TypeError
to prevent unintended implicit coercion causing loss of precision.
Symbols
throw a
TypeError
Objects are first
converted to a primitive
by calling their
[Symbol.toPrimitive]()
(with
"number"
as hint),
valueOf()
, and
toString()
methods, in that order. The resulting primitive is then converted to a BigInt.
The best way to achieve nearly the same effect in JavaScript is through the
BigInt()
function:
BigInt(x)
uses the same algorithm to convert
, except that
Numbers
don't throw a
TypeError
, but are converted to BigInts if they are integers.
Note that built-in operations expecting BigInts often truncate the BigInt to a fixed width after coercion. This includes
BigInt.asIntN()
BigInt.asUintN()
, and methods of
BigInt64Array
and
BigUint64Array
BigInt()
Returns primitive values of type BigInt. Throws an error when called with
new
BigInt.asIntN()
Clamps a BigInt value to a signed integer value, and returns that value.
BigInt.asUintN()
Clamps a BigInt value to an unsigned integer value, and returns that value.
These properties are defined on
BigInt.prototype
and shared by all
BigInt
instances.
BigInt.prototype.constructor
The constructor function that created the instance object. For
BigInt
instances, the initial value is the
BigInt
constructor.
BigInt.prototype[Symbol.toStringTag]
The initial value of the
[Symbol.toStringTag]
property is the string
"BigInt"
. This property is used in
Object.prototype.toString()
. However, because
BigInt
also has its own
toString()
method, this property is not used unless you call
Object.prototype.toString.call()
with a BigInt as
thisArg
BigInt.prototype.toLocaleString()
Returns a string with a language-sensitive representation of this BigInt value. Overrides the
Object.prototype.toLocaleString()
method.
BigInt.prototype.toString()
Returns a string representing this BigInt value in the specified radix (base). Overrides the
Object.prototype.toString()
method.
BigInt.prototype.valueOf()
Returns this BigInt value. Overrides the
Object.prototype.valueOf()
method.
js
function isPrime(n) {
if (n < 2n) {
return false;
if (n % 2n === 0n) {
return n === 2n;
for (let factor = 3n; factor * factor <= n; factor += 2n) {
if (n % factor === 0n) {
return false;
return true;

// Takes a BigInt value as an argument, returns nth prime number as a BigInt value
function nthPrime(nth) {
let maybePrime = 2n;
let prime = 0n;

while (nth >= 0n) {
if (isPrime(maybePrime)) {
nth--;
prime = maybePrime;
maybePrime++;

return prime;

nthPrime(20n);
// 73n
Note:
The
isPrime()
implementation is for demonstration only. For a real-world application, you would want to use a heavily memoized algorithm such as the
Sieve of Eratosthenes
to avoid repeated calculations.