Javascript 在 map() 函数中使用函数 Number() 将字符串转换为数字

Question

我想转换对象数组 watchList 中给出的 imdb 评级。我正在尝试使用 map 功能，但它没有发生。 newList 只给出旧列表，没有任何变化。我做错了什么？

var watchList = [
                {  

                   "Metascore": "74",
                   "imdbRating": "8.8",
                   "imdbVotes": "1,446,708",
                   "imdbID": "tt1375666",
                   "Type": "movie",
                   "Response": "True"
                },
                {  
                   "Metascore": "74",
                   "imdbRating": "8.6",
                   "imdbVotes": "910,366",
                   "imdbID": "tt0816692",
                   "Type": "movie",
                   "Response": "True"
                },
                {
                   "Metascore": "82",
                   "imdbRating": "9.0",
                   "imdbVotes": "1,652,832",
                   "imdbID": "tt0468569",
                   "Type": "movie",
                   "Response": "True"
                }
];



let newList=[];
newList=watchList.map(function(list){
  Number(list.imdbRating);
  return list;
});
console.log(newList);

Answer 1

只是声明 Number 不会改变原始值。如果您希望对象的属性的 imdbRating 是一个数字，您必须分配它。

var watchList=[{"Metascore":"74","imdbRating":"8.8","imdbVotes":"1,446,708","imdbID":"tt1375666","Type":"movie","Response":"True"},{"Metascore":"74","imdbRating":"8.6","imdbVotes":"910,366","imdbID":"tt0816692","Type":"movie","Response":"True"},{"Metascore":"82","imdbRating":"9.0","imdbVotes":"1,652,832","imdbID":"tt0468569","Type":"movie","Response":"True"}];

watchList.forEach(function(list){
  list.imdbRating = Number(list.imdbRating);
});
console.log(watchList);

请注意，在 Javascript 中对象是通过引用传递的 - 更改对象引用中的某些内容将更改原始对象，这就是为什么我使用 forEach 而不是 .map。如果您想创建全新的对象(而不是改变原始对象)，请使用对象传播以及 map:

var watchList=[{"Metascore":"74","imdbRating":"8.8","imdbVotes":"1,446,708","imdbID":"tt1375666","Type":"movie","Response":"True"},{"Metascore":"74","imdbRating":"8.6","imdbVotes":"910,366","imdbID":"tt0816692","Type":"movie","Response":"True"},{"Metascore":"82","imdbRating":"9.0","imdbVotes":"1,652,832","imdbID":"tt0468569","Type":"movie","Response":"True"}];

const newList = watchList.map(({ imdbRating, ...rest }) => ({
  imdbRating: Number(imdbRating),
  ...rest,
}));
console.log(newList);