JS else/else

Question

var movies =
[ 
  {
    title: "Shawshank",
    rating: 5,
    hasWatched: true
  },
  {
    title: "Boardwalk empire",
    rating: 5,
    hasWatched: true
  },
  {
    title: "bladerunner",
    rating: "unkown",
    hasWatched: false
  },
  {
    title: "Ratatouille",
    rating: 4,
    hasWatched: true
  }
]

for(var i = 0; i <movies.length; i++)
{
if(movies[i].hasWatched)
  {
      console.log("You have seen " + movies[i].title + " - " + 
  movies[i].rating);
  }
else (movies[i].hasWatched !== true)
  {
      console.log("You have not seen " + movies[i].title + " - " + 
  movies[i].rating);
  }
}

当我将else-if更改为else时，它将生成以下输出：

• 你见过肖申克-5
• 你没见过肖申克-5
• 你看过木板路帝国-5
• 你还没见过木板路帝国-5
• 你还没见过布莱德伦
• 你见过拉托维尔-4
• 你还没见过拉托维尔-4

为什么在这种情况下，代码似乎会失败呢？

我特别感兴趣的是为什么bladerunner只输出一个。唯一明显的区别是，评级属性是"string“而不是"number”。

最好的

Answer 1

else语句不使用条件表达式。else语句后面的表达式无条件地执行。

在本例中：

其他(moviesi.haswatched !== true) {console.log(“您没有看到”+ moviesi.title +“-”+ moviesi.rating)；}

else语句将执行表达式(movies[i].haswatched !== true)，它没有任何效果。这就像一个声明foo === true;。它被解释，执行，它对程序没有任何影响。

发布的代码相当于我添加的分号，以澄清语句的结尾：

for(var i = 0; i <movies.length; i++)
{
  if(movies[i].hasWatched)
  {
      console.log("You have seen " + movies[i].title + " - " + 
  movies[i].rating);
  }
  else (movies[i].hasWatched !== true);

  console.log("You have not seen " + movies[i].title + " - " + movies[i].rating);
}

也就是说，总是执行最后一个console.log语句。

你可能打算这样写：

if (movies[i].hasWatched) {
  // ...
} else {
  // ...
}

Answer 2

您需要一个if来检查另一个条件

} else if (movies[i].haswatched !== true)
//     ^^

或者省略该条件，因为您已经用一个真正的条件检查了条件，那么您只需要对else部件使用反向条件进行新的检查。

} else {
    //...
}

​

var movies = [{ title: "Shawshank", rating: 5, hasWatched: true }, { title: "Boardwalk empire", rating: 5, hasWatched: true }, { title: "bladerunner", rating: "unkown", hasWatched: false }, { title: "Ratatouille", rating: 4, hasWatched: true }],
    i;

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

​

Answer 3

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

只使用其他方法，而不是给出另一个条件。它将解决以下问题:)