-1 is returned by findIndex() method when nothing is found.

Author: hjcasayas

1-js/05-data-types/05-array-methods/article.md

@@ -305,7 +305,7 @@ In real life arrays of objects is a common thing, so the `find` method is very u
 
 Note that in the example we provide to `find` the function `item => item.id == 1` with one argument. Other arguments of this function are rarely used.
 
-The [arr.findIndex](mdn:js/Array/findIndex) method is essentially the same, but it returns the index where the element was found instead of the element itself.
+The [arr.findIndex](mdn:js/Array/findIndex) method is essentially the same, but it returns the index where the element was found instead of the element itself and returns `-1` when nothing is found.
 
 ### filter