使用Javascript计算数组中重复元素的数量

function countDuplicates(arr) {
  var count = {};
  
  // 计算每个元素的出现次数
  arr.forEach(function(element) {
    if (count[element]) {
      count[element]++;
    } else {
      count[element] = 1;
    }
  });
  
  var result = [];
  
  // 将元素及其计数存储在新数组中
  for (var key in count) {
    result.push({
      element: key,
      count: count[key]
    });
  }
  
  return result;
}

var arr = [1, 2, 3, 2, 4, 1, 5, 1];
var duplicates = countDuplicates(arr);
console.log(duplicates);

[
  { element: '1', count: 3 },
  { element: '2', count: 2 },
  { element: '3', count: 1 },
  { element: '4', count: 1 },
  { element: '5', count: 1 }
]