变量在Promise.then()内的for循环之后不可用

function processItems(items) {
  return new Promise((resolve, reject) => {
    let results = [];
    items.forEach((item, index) => {
      new Promise((resolveInner) => {
        // 模拟异步操作
        setTimeout(() => {
          resolveInner(item * 2);
        }, 100);
      }).then((result) => {
        results[index] = result;
        if (results.length === items.length) {
          resolve(results);
        }
      });
    });
  });
}

processItems([1, 2, 3]).then((results) => {
  console.log(results); // [2, 4, 6]
});

function processItems(items) {
  return new Promise((resolve, reject) => {
    let results = [];
    items.forEach((item) => {
      let index = items.indexOf(item);
      new Promise((resolveInner) => {
        // 模拟异步操作
        setTimeout(() => {
          resolveInner(item * 2);
        }, 100);
      }).then((result) => {
        results[index] = result;
        if (results.length === items.length) {
          resolve(results);
        }
      });
    });
  });
}

processItems([1, 2, 3]).then((results) => {
  console.log(results); // [2, 4, 6]
});

async function processItems(items) {
  let results = [];
  for (let item of items) {
    let result = await new Promise((resolve) => {
      // 模拟异步操作
      setTimeout(() => {
        resolve(item * 2);
      }, 100);
    });
    results.push(result);
  }
  return results;
}

processItems([1, 2, 3]).then((results) => {
  console.log(results); // [2, 4, 6]
});