Roman Numeral Converter works for all numbers except the ones ending in 9

JavaScript
1

Can someone explain why my code works for every number except the ones ending in 9?

Code:

function convertToRoman(num) {
    //declare a holder variable to be used for storing roman num
    var romanNum = "";


    while (num > 0){
        console.log(num)
            if (num >= 1000){
            num -= 1000;
            romanNum += "M";
            } else if (num >= 900){
            num -= 900;
            romanNum += "CM";
            } else if (num >= 500){
            num -= 500;
            romanNum += "D";
            } else if(num >= 400){
            num -= 400;
            romanNum += "CD";
            } else if (num >= 100){
            num -= 100;
            romanNum += "C";
            } else if (num >= 90){
            num -= 90;
            romanNum += "XC";
            } else if (num >= 50){
            num -= 50;
            romanNum += "L";
            } else if (num >= 40){
            num -= 40;
            romanNum += "XL";
            } else if (num >= 10){
            num -= 10;
            romanNum += "X";
            } else if (num == 9){
            num -= 9;
            romanNum = "IX";
            }else if (num >= 5){
            num -= 5;
            romanNum += "V";
            }else if (num == 4){
            num -= 4;
            romanNum += "IV";
            } else if (num >= 1){
            num -= 1;
            romanNum += "I";
            };
    }
    return romanNum;
}

I know the code is far from optimal, but I wanted to solve it with a basic solution first. However it can’t pass the tests ending in 9.

Thank you in advance!

2

Why doesn’t your code end with an else?
The guide trough the use of else/if else may be of use tto you here
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-javascript/introducing-else-statements

3

Little error. You’re missing a + sign.

Change romanNum = "IX";

To romanNum += "IX";