The following code throws an error in javascript:
console.log(String(+0n))But this code runs successfully:
console.log(String(-0n))Why +0n throws an error but -0n does not?
So that it doesn't break asm.js:
- Unary
+followed by an expression is always either a Number, or results in throwing. For this reason, unfortunately,+on a BigInt needs to throw, rather than being symmetrical with+on Number: Otherwise, previously "type-declared" asm.js code would now be polymorphic.
As Bergi highlights in the comments, this was the least bad of three options:
+BigInt -> BigInt: breaks asm.js, and anything else that made the assumption "unary plus gives a Number";+BigInt -> Number: conflicts with the design decision to disallow implicit conversions between Number and BigInt; or+BigInt -> error.+0n is treated as +(BigInt(0)), since unary + means "cast to integer", and it can't automatically do that (for some reason)
console.log(+(BigInt(0)));-0n is treated as BigInt(-0), since negative numbers can be big integers
(You need to check your console for this, since I guess there's a bug in the StackSnippets preventing BigInts from being casted to a string in the console.log call)
console.log(BigInt(-0));