8 years later, https://github.com/tc39/proposal-bigint#state-of-the-proposal

"BigInt has been shipped in Chrome and is underway in Node, Firefox, and Safari."

BigInt: Arbitrary precision integers in JavaScript:

BigIntis a new primitive that provides a way to represent whole numbers larger than2, which is the largest number Javascript can reliably represent with the^{53}Numberprimitive.

But the tragic historical fact that until now, all Javascript numbers were floats means that it's impossible to implement this backward-compatibly without significant syntactic warts:

Many (all?) other dynamically typed programming languages which have multiple numeric types implement a

numeric tower.This forms an ordering between types -- on the built-in numeric types, when an operator is used with operands from two types, the greater type is chosen as the domain, and the "less general" operand is cast to the "more general" type. Unfortunately, as the previous example shows, there is no "more general" type between arbitrary integers and double-precision floats. The typical resolution, then, is to take floats as the "more general" type.Silently losing precision sometimes may be a problem, but in most dynamically typed programming languages which provide integers and floats, integers are written like

1and floats are written like1.0. It's possible to scan code for operations which may introduce floating point precision by looking for a decimal point. JavaScript exacerbates the scope of losing precision by making the unfortunate decision that a simple literal like1is a float. So, if mixed-precision were allowed, an innocent calculation such aswould produce the float 2n ** 53n + 1-- defeating the core functionality of this feature. 2 ** 53To avoid this problem, this proposal bans implicit coercions between

Numbers andBigInts, including operations which are mixed type.throws a 1n + 1TypeError. So does passing1nas an argument into any JavaScript standard library function or Web API which expects aNumber. Instead, to convert between types, an explicit call toNumber()orBigInt()needs to be made to decide which domain to operate in.returns 0 === 0nfalse.

That's all well and good, but obviously the burning questions that I want the answers to are, "What is MOST-POSITIVE-BIGNUM, and how long does it take the Javascript console to print it?"

I wasn't able to figure out which of the several BigInt Javascript packages out there most closely resemble this spec, nor was I able to figure out which of them is the one being used by Chrome. But I assume that they are all representing the bits of the BigInt inside an array (whose cells are either `uint32` or IEEE-754 floats) which means that the gating factor is the range of the integer representing the length of an array (which by ECMA is `2^32-1`). So the answer is probably within spitting distance of either`
2 ^{32(232)} `

`2`.

^{53(232)}As a first attempt, typing` 10n ** 1223146n - 1n `into Chrome's JS console made it go catatonic for a minute or so, but then it spat out a string of 1,223,147 nines. (Fortunately it truncated it rather than printing them all.) So that's bigger than the Explorer version!

... and maybe we have a winner, or at least a lower bound on the max?> (2n ** 32n - 1n) ** (2n ** 32n - 1n)

× Uncaught RangeError: Maximum BigInt size exceeded

> (2n ** 32n - 1n) ** (2n ** 31n - 1n)

× Uncaught RangeError: Maximum BigInt size exceeded

> (2n ** 32n - 1n) ** (2n ** 30n - 1n)

That last one has made Chome sit there chewing four CPU-hours so far, so it's either still doing the exponentiation, or it's trying to grind it to decimal. If it ever comes back with a result, I'll update this post...

**Update:** After 87 hours, I stopped waiting.

Previously, previously, previously, previously, previously, previously.