<script>
function rand_nums(min,max,count){
    var arr = [];
    for(var i=min;i<max;i++){
        arr.push(i);
    }
    var nums = [];
    var temp = 0;
    for(var i=0;i<count;i++){
        var j = Math.floor((Math.random()*(count -i)+i));
        temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        nums[i] = arr[i];
    }
    return nums;
}

var arr = rand_nums(0,5000,5000);
console.log(arr.length)

//test
function unique(arr) {
  var obj = {}; 
  arr.forEach(function(v,i) {
    obj[v] = 1
  });
 
  return Object.keys(obj)
}
console.log(unique(arr).length);
</script>