I believe this is optional since:

1. I attached the chorus:

    Never gonna give you up
    Never gonna let you down
    Never gonna run around and desert you
    Never gonna make you cry
    Never gonna say goodbye
    Never gonna tell a lie and hurt you 

2. The first example test case is a check for support of all strings with indices from 0 to 5 inclusive.

Thanks for your suggestion.

Maybe you can mention that the passed numbers are between 0 and 5?

I recognized one thing
console.log(twoSum([738, 523, 783, 0, 104, 261, 90, 369, 24, 547], 369));

It does only return [3], but the solutions is [3,7]. For some reason even it satisfied the condition in find method, it would return the falsy value (For what I have tested the case with 0).

What could be wrong with my algorithm? It would be helpful, if you could point out how I implemented it wrongly. Thanks!

Eventhough I should have the correct output

How do you know that? You've implemented a wrong algorithm, and I think the implementation is wrong too. Not an issue.

Ah, because then the indexes wouldn't line up with the original anymore.. right!

You're not supposed to sort the input.