如何在一个数组中返回重复三次的数组？

function findTripleDuplicates(arr) {
  var result = [];
  
  for (var i = 0; i < arr.length; i++) {
    var count = 0;
    
    for (var j = 0; j < arr.length; j++) {
      if (arr[j] === arr[i]) {
        count++;
      }
    }
    
    if (count === 3) {
      result.push(arr[i]);
    }
  }
  
  return result;
}

var array = [1, 2, 3, 4, 5, 2, 3, 4, 6, 7, 8, 9, 7, 8, 9];
var tripleDuplicates = findTripleDuplicates(array);
console.log(tripleDuplicates);