Thanks for the answer. I checked my browser's setting, but it's already set to UTF-8.
Would you say it's likely not something wrong with my code cause when I console.log out the input message, it's all messed up?

Can someone please help me with the Katakana cases?

All my other cases are fine.

The Katakana case shows up like this, and I have no clue what's going on cause of the wierd alphabets. I'm almost hypothesizing it's something to do with me not having the font on my computer.

encode(カタカã)ƒŠ

Expected: タモタワ, instead got: タコタア

decode (タモタワ)

Expected: カタカナ, instead got: カタカア

I had to just manually make the program produce [] when the input is a string or a non-integer....