Javascript 为什么.forEach在express.js中在我的控制器中调用后返回未定义？

我有一个包含对象的数组，每个对象都有一个名为avgRating的属性，带有一个浮点数或整数。例如：

const movies = [
  {
    name: 'Rambo I', avgRating: 4.6659
  },
  {
    name: 'Rambo II', avgRating: 3.158
  },
  {
    name: 'Rambo III', avgRating: 3.956
  }
];

在util.js文件中，我有一个函数，可以将每部电影的AVG四舍五入到最接近的0.5或整数中：

exports.roundingAvgRating =  (movies) => {
  const moviesCopy = [...movies];
  return moviesCopy.forEach((movie) => {
    if (movie.avgRating === null) {
      movie.avgRating = null
    } else {
      movie.avgRating = Math.round(movie.avgRating * 2) / 2;
    }
  });
};

问题是，当我在我的控制器中调用函数时，它返回undefined

const { roundingAvgRating } = require('../utils/roundingAvgRatings.js');
const roundedRatings = roundingAvgRating(searchItems)
console.log(roundedRatings) // undefined...why?

---

您希望映射您的电影，并且应该在循环中每次返回电影。像这样：

const movies = [
  {
    name: 'Rambo I', avgRating: 4.6659
  },
  {
    name: 'Rambo II', avgRating: 3.158
  },
  {
    name: 'Rambo III', avgRating: 3.956
  }
];

const roundingAvgRating = (movies) => {
  

  return movies.map((movie) => {
    if (movie.avgRating) {
       movie.avgRating = Math.round(movie.avgRating * 2) / 2;
    }
    return movie
  });
}

---

另外，您不需要在map中进行复制，forEach将不会返回任何您希望它返回的内容？因为总是返回未定义的内容。我希望在运行const roundedRatings=roundingAvgRatingsearchItems时，然后roundedRatings应该是具有圆角的数组avgRatings@Lomono-听起来像您想要的：movies=>movies.map{avgRating}=>avgRating==null？空：Math.roundavgRating*2/2；

return movies.map((movie) => {
  if (movie.avgRating) {
     movie.avgRating = Math.round(movie.avgRating * 2) / 2;
  }
  return movie;
});