Javascript计数出现次数

function countOccurrences(arr, target) {
  return arr.reduce((count, item) => {
    return item === target ? count + 1 : count;
  }, 0);
}

const array = [1, 2, 3, 4, 2, 2, 3];
const target = 2;
console.log(countOccurrences(array, target)); // 输出: 3

function countOccurrences(str, target) {
  let count = 0;
  let index = str.indexOf(target);
  while (index !== -1) {
    count++;
    index = str.indexOf(target, index + 1);
  }
  return count;
}

const string = "hello world, hello universe";
const target = "hello";
console.log(countOccurrences(string, target)); // 输出: 2

function countOccurrences(arr, target) {
  if (!Array.isArray(arr) || arr.length === 0) return 0;
  return arr.reduce((count, item) => {
    return item === target ? count + 1 : count;
  }, 0);
}

function countOccurrences(arr, target) {
  const map = {};
  arr.forEach(item => {
    if (item === target) {
      map[item] = (map[item] || 0) + 1;
    }
  });
  return map[target] || 0;
}