Is JavaScript's BigInt broken?

Published on 16/08/2025

JavaScript's bigint is quite an unusual and controversial primitive. It was introduced and standardized in ECMAScript in 2020. Its purpose is to easily handle integers of arbitrary size since the number safe integer range is limited to [-(2⁵³ - 1), 2⁵³ - 1].

Despite of its virtues, many people still criticize it because of many issues related to convenience and lack of integration with existing JS standard APIs / libraries.

The virtues of BigInt

Let's first understand what are the virtues and the purpose of bigint. bigint allows us to handle and operate with integers that are beyond the safe integer range of number. bigint has no fixed size, so it's not some 64-bit or 128-bit integer. Its size has no defined limits (in ECMAScript, but different JS engines certainly have). And this is what makes it so powerful. It guarantees that there will never be an integer overflow:

console.log(1000_000_000_000_000_000_000n ** 6n); // 1 and 126 zeroes

bigint numbers support many integer operations (including integer arithmetic and bitwise operations, except >>>) that you would expect from normal integers:

console.log(1n + 10n); // 11n
console.log(10n - 2n); // 8n
console.log(10n * 3n); // 30n
console.log(11n / 2n); // 5n, integer division
console.log(1000_000_000_000_000_000n << 2n); // 4000000000000000000n
console.log(3n & 5n); // 1n
console.log(3n | 5n); // 7n
console.log(3n ^ 5n); // 6n
console.log(~5n); // -6n
console.log(1000n ** 5n); // 1000000000000000n
console.log(1000n / 0n); // division by zero error

The problems with BigInt

Despite of this, bigint has several inconveniences. Which I'll discuss here.

Mixed BigInt and Number expressions are illegal

JavaScript doesn't allow mixed bigint and number expressions (exceptions are comparisons: ==, ===, <, etc). If an expression contains both number and bigint an error will occur:

console.log(1n * 1); // Exception

This means bigintnumbers won't be automatically converted to floating point numbers similarly to many other programming languages when the expression contains mixed integers and floating point numbers. This decision was made because of potential precision losses and also because bigint numbers can have larger absolute values than the maximum number finite absolute value (2¹⁰²⁴ - 2⁹⁷¹, or ~ 1.7976931348623157E+308).

Fortunately, you can still manually convert bigint to number and vice versa by using functions Number() and BigInt():

console.log(Number(10n) * 4); // 40
console.log(BigInt(6) * 4n); // 24n

No Math support

Another inconvenience is that Math functions / utilities largely don't work with bigint numbers. Even Math.max() doesn't work with bigint:

console.log(Math.max(1n, 2n)); // Exception

There is a proposal to add a math standard library for BigInt. Hopefully it will become a reality one day.

No JSON support

The lack of JSON support is another painful point. There is no bigint type in JSON. Also, if you try to call JSON.stringify() for something that contains a bigint value, an exception will occur:

const obj = {
	prop: 1n,
};

console.log(JSON.stringify(obj)); // Exception

One workaround for this is to convert bigint numbers to strings by passing the replacer callback to JSON.stringify():

const obj = {
	prop: 1n,
};

console.log(
	JSON.stringify(obj, (key, value) => typeof value === "bigint" ? value.toString() : value)
); // {"prop":"1"}

When parsing the JSON with JSON.parse() we can pass the reviver callback where we can convert the stringified bigint back to bigint for known properties:

console.log(JSON.parse(
	'{"prop":"138","otherProp":"789"}', 
	(key, value) => key === "prop" && typeof value === "string" ? BigInt(value) : value
)); // { prop: 138n, otherProp: "789" }

Not ideal and complicated for parsing when dealing with deep objects, but it works.

Worse performance

Yes, unfortunately. In addition to these inconveniences, bigint operations are generally slower than for number. The reasons are:

Arbitrary precision. number fits in a 64-bit float and most ops use single CPU instructions. bigint values are variable-length "bignums" stored on the heap. Operations scale with the number of "limbs" (O(N) for add/sub, super-linear (up to O(N²)) for multiplications and divisions).
Allocation & GC. Many bigint ops create new heap objects. In contrast, number values are typically unboxed registers.
Fewer JIT fast paths. Engines have decades of tricks for regular numbers and typed arrays. bigint paths are more specialized and can't leverage hardware FP units.

Conclusion

So is bigint broken and poorly designed? I would say "largely no". number has a very large safe integer range of [-(2⁵³ - 1), 2⁵³ - 1] for most general real world problems. Yes, it would be better if it was a true signed 64-bit number. But number safe integer range is only about ~1000 times smaller (on a logarithmical scale it's not that bad) than the range of a 64-bit signed integer. So just don't use bigint if you don't really need it. bigint is not designed for general usage.

bigint absolutely has valid (and growing) use-cases (such as 64-bit IDs from databases and services, timestamps and durations with nanosecond precision, cryptography, finance, etc.). It's just not a drop-in replacement for number, so it shines in specific domains where correctness and arbitrary precision are the highest priority.