New camper asks if his solution is elegant or not

Hi, am a begginer at Javascript programming. I would like to ask experienced programmers to check, whether my solution to the ** Roman Numeral Converter** project is elegant in terms of problem solving.
My code:

function convertToRoman(num) {
    let one="I",five="V",ten="X";
    
    function getCombinationElement(power){
        switch (power){
            case 1:
                one="I";
                five="V";
                ten="X";
                break;
            case 2:
                one="X";
                five="L";
                ten="C";
                break;
            case 3:
                one="C";
                five="D";
                ten="M";
                break;
            case 4:
                one="M";
                five="v";
                ten="x";
                break;
        }
        return {
            "0":"",
            "1":one,
            "2":one+one,
            "3":one+one+one,
            "4":one+five,
            "5":five,
            "6":five+one,
            "7":five+one+one,
            "8":five+one+one+one,
            "9":one+ten
        }
    }
    
    let roman="";
    let splittedNum=num.toString().split("");
    for (let i=0;i<splittedNum.length;i++){
        splittedNum[i]=parseInt(splittedNum[i]);
    }
    for (let i=0;i<splittedNum.length;i++){
        roman+=(getCombinationElement(splittedNum.length-i)[splittedNum[i]]);
        
    }
    console.log(roman);
    return roman;
}

convertToRoman(400);

If not, what could I improve?
Thanks in advance!