Difference Between indexOf and findIndex function of array

Question

I am confused between the difference between the two function indexOf and find Index in an array.

The documentation says

findIndex - Returns

Answer 1

Another difference is that with findIndex() the user can apply some function and find the element in the array which passes the test.

But the same is not true with indexOf() operator. A user can just check whether the particular element exists in the array or not.