That one is a side effect of how the combination of Array.prototype.map and parseInt work - the former calls it's argument with (value, index, array) repeatedly, parseInt expects (value, base) where 2 <= base <= 36, or it returns NaN (ecma-262 1e, 15.1.2.2 "parseInt(string, radix)").
Most of the array iteration methods (forEach, map, every, some) pass 3 arguments; I believe reduce passes 4.
Oh, I see now. There is a conflict between the two parameters (index and base). Since the code you mentioned returns [0, NaN, NaN], why does it return 0 in the "zeroth" element of the array? What even is a base 0 number to JavaScript?
As I experimented on passing in 0 as an argument for the base parameter of parseInt, I found that it works normally. Why would that work? Is it just all in the spec?
From MDN (radix being the same as base with the previously used verbage):
If radix is undefined or 0 (or absent), JavaScript assumes the following:
If the input string begins with "0", radix is eight (octal) or 10 (decimal). Exactly which radix is chosen is implementation-dependent. ECMAScript 5 specifies that 10 (decimal) is used, but not all browsers support this yet. For this reason always specify a radix when using parseInt.
You do have to be careful with things like
Oh, wow. This is indeed weird. I didn't know this was an outlier.
Why does this happen? Are there any other outliers I should be aware of so I could update the article to mention them?
That one is a side effect of how the combination of
Array.prototype.mapandparseIntwork - the former calls it's argument with(value, index, array)repeatedly, parseInt expects(value, base)where2 <= base <= 36, or it returns NaN (ecma-262 1e, 15.1.2.2 "parseInt(string, radix)").Most of the array iteration methods (forEach, map, every, some) pass 3 arguments; I believe reduce passes 4.
Oh, I see now. There is a conflict between the two parameters (
indexandbase). Since the code you mentioned returns[0, NaN, NaN], why does it return0in the "zeroth" element of the array? What even is a base 0 number to JavaScript?As I experimented on passing in
0as an argument for thebaseparameter ofparseInt, I found that it works normally. Why would that work? Is it just all in the spec?From MDN (
radixbeing the same asbasewith the previously used verbage):Thanks for looking into this! We appreciate your efforts. I'll go make a quick edit to the article now to raise this point.
Ah, thanks for this example! It was fun digging into this.