romantoint.js

/**
 * @param {string} s
 * @return {number}
 */
var romanToInt = function (s) {

    const base = {
        I: 1,
        V: 5,
        X: 10,
        L: 50,
        C: 100,
        D: 500,
        M: 1000,
    };

    const sArr = s.split('');
    let value = 0;
    sArr.forEach((item, index) => {
        let curr = base[sArr[index]]
        let next = base[sArr[index + 1]]

        curr < next ? value -= curr : value += curr
    });

    return value
};

console.log(romanToInt('III'))
console.log(romanToInt('XXV'))
console.log(romanToInt('IX'))
console.log(romanToInt('MMDC'))
console.log(romanToInt('DC'))