Find Index of duplicate elements in an Array.

var a = [1,3,4,2,1,6,3,8,10,9,7,2,3,4,5,6,3,2,6,7,8,1,3,9];
console.log(a);
console.log(a.length);

function findAll(a,x){
  var res = [];
  var pos = 0;
  var len = a.length;
  while(pos<len){
    pos = a.indexOf(x,pos);
    if(pos == -1)break;
    res.push(pos);
    pos = pos+1;
  }
  if(res.length ==0){console.log("Element not found");}
  return res;
}
console.log("Indexes of 1: "+ findAll(a,1).join());
console.log(findAll(a,2));
console.log(findAll(a,3));
console.log(findAll(a,100));