function div_mod(a, b)  
 {  
  if (b <= 0)   
    throw new Error("b cannot be zero. Undefined.");  
  if (isInt(a) && !isInt(b))  
    throw new Error("A or B are not integers.");  
  return [Math.floor(a / b), a % b];  
}  
function isInt(n) {  
  return n % 1 === 0;  
}  
console.log(div_mod(17, 4));