JavaScript Sort based on external object

Question

I'm trying to sort a list of objects based on the appearance of a key in an external object. For some reason, I'm not able to sort the array and I tried using lodash or other methods..

Here's a more simple example:

arr = [1, 2, 3, 4, 5, 6]
obj = { 4: true, 6: true }

arr.sort((a, b) => obj[a] - obj[b])
// [1, 2, 3, 4, 5, 6]

I would like the truth-y values to be first, as in [4, 6, 1, 2, 3, 5]

Why doesn't this work?

AKX · Accepted Answer · 2021-08-12 11:15:27Z

3

You can't subtract true and undefined (which is the value for keys that don't exist).

> arr.sort((a, b) => (obj[b] || 0) - (obj[a] || 0))
(6) [4, 6, 1, 2, 3, 5]

works instead (i.e. coercing that undefined to zero).

answered Aug 12, 2021 at 11:15

AKX

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