CountDiv.js

function solution(A, B, K) {
    // write your code in JavaScript (Node.js 8.9.4)
    if(K==0) return 0;
    const a = Math.floor(A/K);
    const b = Math.floor(B/K);
 
    if(a==0 && b==0 && B != 0)
      return 0;
      
    let between = b - a;
    if(A%K==0) 
      between++;

    return between;
}