“ for”循环未正确遍历对象数组

Question

当我运行非常简单的以下代码时，由于某种原因，我在浏览器控制台中得到以下结果：“ 6您尚未观看未定义的未定义。” 谁能指出我的错误？

 var movies = [{ title: "The Mummy", hasWatched: true, stars: "5 stars" }, { title: "About A Boy", hasWatched: true, stars: "5 stars" }, { title: "It", hasWatched: false, stars: "5 stars" }, { title: "Cleopatra", hasWatched: false, stars: "5 stars" } ]; for (var i = 0; i <= movies.length; i++) { if (movies.hasWatched) { console.log("You have watched " + movies.title + " " + movies.stars + "."); } else { console.log("You have not watched " + movies.title + " " + movies.stars + "."); } } 

Answer 1

您有一个对象数组，因此您需要引用每个数组元素的索引。 您还需要将循环减少一，因为数组索引是从零开始的，但是长度不是。

 var movies = [{ title: "The Mummy", hasWatched: true, stars: "5 stars" }, { title: "About A Boy", hasWatched: true, stars: "5 stars" }, { title: "It", hasWatched: false, stars: "5 stars" }, { title: "Cleopatra", hasWatched: false, stars: "5 stars" } ]; for (var i = 0; i < movies.length; i++) { if (movies[i].hasWatched) { console.log("You have watched " + movies[i].title + " " + movies[i].stars + "."); } else { console.log("You have not watched " + movies[i].title + " " + movies[i].stars + "."); } } 

Answer 2

将for条件更改for i < movies.length ; 你有一个额外的迭代。 并且您还需要引用movie movies[i]以获得实际的电影，例如， movies[i].title 。

在上面的示例中，最后一个索引为3（项目编号为0、1、2、3），但是您的循环将进行到4，并将尝试查找movies[4].title并返回未定义。

Answer 3

for (var i = 0; i <= movies.length; i++) {
  if (movies[i].hasWatched) {
    console.log("You have watched " + movies[i].title + " " + movies[i].stars + ".");
 } else {
    console.log("You have not watched " + movies[i].title + " " + movies[i].stars + ".");
  }

}

您只是在访问时缺少索引标识符