JS:计算数组中元素的频率

function calculateFrequency(arr) {
  var frequency = {};
  
  for (var i = 0; i < arr.length; i++) {
    var element = arr[i];
    
    if (frequency[element]) {
      frequency[element]++;
    } else {
      frequency[element] = 1;
    }
  }
  
  return frequency;
}

var array = [1, 2, 3, 2, 1, 3, 1, 2, 3, 4];
var result = calculateFrequency(array);
console.log(result);

{
  1: 3,
  2: 3,
  3: 3,
  4: 1
}