如何计算数组中每个项目的出现次数？[重复]

无需使用jQuery即可完成此任务-此示例将构建一个对象，其中包含数组中每个不同元素的出现次数

O(n)

var occurrences = { };for (var i = 0, j = arr.length; i < j; i++) {   occurrences[arr[i]] = (occurrences[arr[i]] || 0) + 1;}console.log(occurrences);        // {ab: 3, pq: 1, mn: 2}console.log(occurrences['mn']);  // 2

var occurrences = arr.reduce(function(obj, item) {  obj[item] = (obj[item] || 0) + 1;  return obj;}, {});console.log(occurrences);        // {ab: 3, pq: 1, mn: 2}console.log(occurrences['mn']);  // 2