[рони]

var arr = new Array(10000).fill(1)

let threeF = arr => arr.filter(el => {
  this[el] = ++this[el] || 1;
  return 3 === this[el]
}, {})
console.time("x")
var x = threeF(arr);
console.timeEnd("x")


function fn(d, e) {
    for (var f = [], b = {}, a, c = 0; c < d.length; c++)
    a = d[c], b[a] == e || (b[a]++ || (b[a] = 1), b[a] == e && f.push(a));
    return f
};

console.time("k")
var k = fn(arr,3);
console.timeEnd("k")