script.js

const arabicInput = document.getElementById("arabicInput");
const romanInput = document.getElementById("romanInput");

arabicInput.addEventListener("input",(e)=>{
    romanInput.value = arabicToRoman(e.target.value);
});
romanInput.addEventListener("input",(e)=>{
    arabicInput.value = romanToArabic(e.target.value);

});

function arabicToRoman(number){
    let roman = "";
    const romanNumList = {M:1000,CM:900, D:500,CD:400, C:100, XC:90,L:50, XV: 40, X:10, IX:9, V:5, IV:4, I:1};
    let a;
    if(number > 3999)
        return "Enter a number between 1 and 3999";
    else{
        for(let key in romanNumList){
            a = Math.floor(number / romanNumList[key]);
            if(a >= 0){
                for(let i = 0; i < a; i++){
                    roman += key;
                }
            }
            number = number % romanNumList[key];
        }
    }

    return roman;
}
function romanToArabic(romanNumber){
    romanNumber = romanNumber.toUpperCase();
    const romanNumList = ["CM","M","CD","D","XC","C","XL","L","IX","X","IV","V","I"];
    const corresp = [900,1000,400,500,90,100,40,50,9,10,4,5,1];
    let index =  0, num = 0;
    for(let rn in romanNumList){
        index = romanNumber.indexOf(romanNumList[rn]);
        while(index != -1){
            num += parseInt(corresp[rn]);
            romanNumber = romanNumber.replace(romanNumList[rn],"-");
            index = romanNumber.indexOf(romanNumList[rn]);
        }
    }
    return num;
}