makes parity with native filter function

[kalpeshsingh]

What was the issue?
The newFilter method allows undefined values to be part of the filtered array but the native implementation removes that.

How to replicate it?
Add numbers[7] = 9 and change condition to filter odd numbers and you will find out that it doesn't filter empty/undefined values in the array.

numbers array would be -

const numbers = [1, 2, 3, 4, undefined, undefined, undefined, 9]

What is the reason?
When we call callback.call(context, this[index], index, this) for undefined value then it produces true and it pushes the value to result array.

undefined => undefined % 2 !== 0 // produces `true`

How to prevent it?
We need to put a guard condition to only allow values that are actually part of the array and not produced artificially. The proposed condition makes sure that it matches with native .filter output.