Array.prototype.reduce() On Arrays Of One Element

In following reduction + map operations, no. 3 is puzzling me. Can anyone please explain why // 1 [1,2,3,4,5].filter(x => x==3).reduce((x, y) => y) // -> 3, all good // 2

Solution 1:

The filtered array contains only one element so reduce will return that value.

Read the docs :

If the array has only one element (regardless of position) and no initialValue was provided, or if initialValue is provided but the array is empty, the solo value would be returned without calling callback.

For more : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce