Question

我有js文件，我用它来学习javascript。但是，当我运行concatAll时，它说：

Uncaught TypeError: movieLists.map(...).concatAll is not a function

Js档案：

console.log(tryFun());

Array.prototype.concatAll = function() {
    var results = [];
    this.forEach(function(subArray) {
        results.push(subArray);
    });

    return results;
};



function tryFun() {
    var movieLists = [
        {
            name: "New Releases",
            videos: [
                {
                    "id": 70111470,
                    "title": "Die Hard",
                    "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
                    "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                    "rating": 4.0,
                    "bookmark": []
                },
                {
                    "id": 654356453,
                    "title": "Bad Boys",
                    "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
                    "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                    "rating": 5.0,
                    "bookmark": [{ id: 432534, time: 65876586 }]
                }
            ]
        },
        {
            name: "Dramas",
            videos: [
                {
                    "id": 65432445,
                    "title": "The Chamber",
                    "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
                    "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                    "rating": 4.0,
                    "bookmark": []
                },
                {
                    "id": 675465,
                    "title": "Fracture",
                    "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
                    "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                    "rating": 5.0,
                    "bookmark": [{ id: 432534, time: 65876586 }]
                }
            ]
        }
    ];

return movieLists.map(movieList=>
        movieList.videos.map(video=>video.id))
.concatAll();
}

看起来我在这里错过了一些技巧。谢谢你看看这个。应该是Javascript没有在它的原型上添加函数，这个函数是在文件开头定义的吗？

Answer 1

您在添加tryFun之前调用了concatAll。调用tryFun之前将方法添加到原型：

＆＃13;
＆＃13;
Array.prototype.concatAll = function() { var results = []; this.forEach(function(subArray) { results.push(subArray); }); return results; }; console.log(tryFun()); function tryFun() { var movieLists = [ { name: "New Releases", videos: [ { "id": 70111470, "title": "Die Hard", "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg", "uri": "http://api.netflix.com/catalog/titles/movies/70111470", "rating": 4.0, "bookmark": [] }, { "id": 654356453, "title": "Bad Boys", "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg", "uri": "http://api.netflix.com/catalog/titles/movies/70111470", "rating": 5.0, "bookmark": [{ id: 432534, time: 65876586 }] } ] }, { name: "Dramas", videos: [ { "id": 65432445, "title": "The Chamber", "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg", "uri": "http://api.netflix.com/catalog/titles/movies/70111470", "rating": 4.0, "bookmark": [] }, { "id": 675465, "title": "Fracture", "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg", "uri": "http://api.netflix.com/catalog/titles/movies/70111470", "rating": 5.0, "bookmark": [{ id: 432534, time: 65876586 }] } ] } ]; return movieLists.map(movieList=> movieList.videos.map(video=>video.id)) .concatAll(); }
＆＃13;
＆＃13;
＆＃13;

但改变内置对象是非常不好的做法 - 最好调用一个独立的函数，或使用你自己的包装器。

Answer 2

哦，明白了！它的程序流程，concatAll从未被添加。只需移动呼叫有助于：

Array.prototype.concatAll = function() {
    var results = [];
    this.forEach(function(subArray) {
        results.push(subArray);
    });

    return results;
};

console.log(tryFun());

Answer 3

通常与您尝试实现的内容相关，您可以在没有.concatAll()函数的情况下轻松过关，因为.concat()是可变参数并会自动展平数组。

因此，使用“传播语法”，您可以执行此操作：

return [].concat(...movieLists.map(
    movieList => movieList.videos.map(video => video.id))
);

这是一个现场演示：

console.log(tryFun());

function tryFun() {
  var movieLists = [{
      name: "New Releases",
      videos: [{
          "id": 70111470,
          "title": "Die Hard",
          "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
          "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
          "rating": 4.0,
          "bookmark": []
        },
        {
          "id": 654356453,
          "title": "Bad Boys",
          "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
          "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
          "rating": 5.0,
          "bookmark": [{
            id: 432534,
            time: 65876586
          }]
        }
      ]
    },
    {
      name: "Dramas",
      videos: [{
          "id": 65432445,
          "title": "The Chamber",
          "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
          "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
          "rating": 4.0,
          "bookmark": []
        },
        {
          "id": 675465,
          "title": "Fracture",
          "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
          "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
          "rating": 5.0,
          "bookmark": [{
            id: 432534,
            time: 65876586
          }]
        }
      ]
    }
  ];

  return [].concat(...movieLists.map(
      movieList => movieList.videos.map(video => video.id))
  );
}

或者您可以使用.reduce()并将.concat()放入回调中。

  return movieLists.reduce(
      (res, movieList) => res.concat(...movieList.videos.map(video => video.id))
  , []);

Answer 4

更简单的尝试下面的代码。

Array.prototype.concatAll = function() {
    var results = [];
    this.forEach(function(subArray) {
        results.push.apply(results, subArray);
    });

    return results;
};
console.log(tryFun());

方法未添加到Prototype

4 个答案: