Well, the CONSOLE returns that because you have a console.log() inside the for loop, that will make it to run again and again until the loop is done. If you actually console.log(); your function, it will return an empty array [ ]. Try it out: console.log(reverseString("hello"));.
Your function doesn’t really return anything, because at the end of the function, you are returning newArray which is an empty string and is not modified in any way