使用forEach查找和更新不起作用

let arr = [1, 2, 3, 4, 5];
arr.forEach((item, index) => {
  if (item === 3) {
    arr[index] = 10; // 直接修改原数组
  }
});
console.log(arr); // 输出: [1, 2, 10, 4, 5]

let arr = [1, 2, 3, 4, 5];
let newArr = arr.map(item => {
  if (item === 3) {
    return 10; // 返回新的值
  }
  return item;
});
console.log(newArr); // 输出: [1, 2, 10, 4, 5]

let arr = [1, 2, 3, 4, 5];
let promises = [];

arr.forEach(item => {
  promises.push(new Promise((resolve) => {
    setTimeout(() => {
      if (item === 3) {
        resolve(10);
      } else {
        resolve(item);
      }
    }, 1000);
  }));
});

Promise.all(promises).then(newArr => {
  console.log(newArr); // 输出: [1, 2, 10, 4, 5]
});