Why doesn't Number throw on BigInts it can't represent precisely?

[tjcrowder]

BigInt throws when given a number it can't represent precisely:

console.log(BigInt(1.2)); // RangeError: The number 1.2 cannot be converted to a BigInt because it is not an integer

Why does Number not throw when given a BigInt it can't represent precisely?

const big = 2n**53n + 1n;
console.log(big);         // 9007199254740993n
console.log(Number(big)); // 9007199254740992

It's not like Number doesn't throw in other cases (Number(Symbol()), Number({valueOf: function() { throw Error(); }}))...

Is it because of the inherently-imprecise nature of Number? And the largely-inherently-precise nature of BigInt? (Although given 5n / 2n === 2n, BigInt isn't always precise...)

#132 and #15 touched on this, but I don't think quite addressed it. Apologies in advance if I've missed it or am being dense, as seems likely.

(To be clear, I'm not saying it should throw on all "unsafe" integers, Number(2n**53n + 2n) should continue to work. Just asking why it doesn't throw when precision loss would occur, like BigInt does.)

[littledan]

There were some important use cases to have an explicit rounding operation, so the Number constructor does that. We debated this question back and forth in various issues on this repository.

[tjcrowder]

Okay, thanks. The inconsistency just tripped me up trying to explain BigInt, hence my (probably sophomoric) attempts to explain above with the "nature" thing. :-) I don't see a discussion of using Number vs. a separate rounding function in the issues, but really that would just be for my curiousity...

[littledan]

Well, maybe we can talk about how the docs can be improved for clarity, cc @sarahgp