Roman to Integer in javascript leetcode problem

const RomanNumber="VII"

const romanToInt=(s)=>{

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

    let res=0;

    s.split('').forEach((num,i)=>{

        if(map[num]<map[s[i+1]]) res-=map[num]

        else res +=map[num]

    });

      return res;

  };

console.log(`${RomanNumber} to integer is  ${romanToInt(RomanNumber)}` );