sure, my bad 🤗

Please use spoiler flag next time.

1. containsDuplicates method returns true or false, !! sign converts to boolean. So you don't need it in this case.
2. you make sort two times. If you will work with array with 1 000 000 000 items, this operation will really slow down your computer.

If you want to make your solution clearier, try to

1. sort keys
2. create new array
3. iterate over keys and push original array's items, like this arr.push(this[keys[i]])
4. return new array