String middle character on JavaScript [closed]

Hi guys I am trying to solve this problem on JavaScript and I am stuck.

Instructions
This function takes a string of at least one character, and it should return the middle character(s) from that string.

If the string is of odd length, the function should return a single character. If the string is of even length, it should return the middle two characters concatenated together.

This is what I tried:

function returnMiddleCharacter(string) {
      
    let letterCount = string.length;
    let midChar = Math.round(letterCount/2)
    
    if (letterCount === 1) {
        return string;
    }
    if(letterCount % 2 !== 0){
        return string[midChar]
    }else{
        string[midChar -1] + string[midChar]

    }

}