Allow sorting NaN values

[Richienb]

When sorting NaN values, they should be treated as the lowest value in the entire array:

const numberSort = require('num-sort');

console.log([1, NaN, 4, 3].sort(numberSort.ascending));
//=> [NaN, 1, 3, 4]

cc @sindresorhus

[papb]

What is the current behavior?

[Richienb]

It currently throws TypeError: Expected a number.

[papb]

What is the reasoning for it being considered lowest rather than highest?

[Richienb]

NaN means not a number which means nothing which means 0.

[papb]

Well but 0 is not the lowest possible number 😅

[Richienb]

0 is the smallest natural number and is usually a fallback for NaN so it's obvious for it to be the smallest number.

[papb]

What do you think should be the expected result for [1, -1, NaN].sort(numberSort.ascending)?

[Richienb]

[NaN, -1, 1]

[papb]

So you're treating NaN as -Infinity, not 0.

My opinion is that this is arbitrary and often not intended. How about, instead, adding an option?

const numberSort = require('num-sort');

console.log([1, NaN, -4, 3].sort(numberSort.ascending({ treatNanAs: -Infinity })));
//=> [NaN, -4, 1, 3]

[sindresorhus]

I agree, NaN should be last, after -Infinity.

[sindresorhus]

So you're treating NaN as -Infinity, not 0.

Infinity is technically a number. NaN is not, hence it should be first/last.

[papb]

@sindresorhus Do you prefer a breaking change (simply change the existing behavior) by arbitrarily choosing between first/last, or do you think an option such as I suggested is possible?

[sindresorhus]

I prefer a breaking change.

[papb]

@sindresorhus One last confirmation:

[1, -1, -Infinity, NaN].sort(numberSort.ascending)
//=> [NaN, -Infinity, -1, 1]

[1, -1, -Infinity, NaN].sort(numberSort.descending)
//=> [1, -1, -Infinity, NaN]

Is this correct? If yes I'll submit a PR

[sindresorhus]

Correct