occurence

function duplicateCount(text){
  const result = {};
  const tab = text.toLowerCase().split('');

    tab.forEach((elem)=>{
        if(elem in result){
            result[elem] = ++result[elem];
        }
        else{
            result[elem] = 1;
        }
    });

return Object.values(result).filter(el => el>1).length


}