如何从 JavaScript 数组中删除项目？

Question

我开始用 JavaScript 学习编码，我们的老师让我们搜索这个网站。我的东西没有答案所以我想问一下。我希望没问题，我已经搜索了很多问题，但找不到任何与我的问题相似的内容。

我的任务是检查我的时间表并找出我最不喜欢的两个科目。这是我的：

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];

我说我想选修西班牙语和历史，我做到了：

for (var i = 0; i < 14; i++) {
   if (subjects[i] == "Spanish") {
   delete subjects[i];
  }
  if (subjects[i] == "History") {
    delete subjects[i];
  }
}

但这表示它有 "empty slots" :

Array [ "Maths", <1 empty slot>, "English", "Science", <1 empty slot>, "Physical Education", <1 empty slot>, "English", "Science", "Maths", 4 more… ]

但它不应该再在那里了。我该怎么做？

Answer 1

正如您所发现的，数组可以是 "sparse"（并非所有索引都必须有值），而这正是您使用 delete 完成的。您删除了数据，但保留了索引。

要完全删除索引，请使用 .splice() method：

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];


for (var i = 0; i < 14; i++) {
   if (subjects[i] == "Spanish") {
   subjects.splice(i, 1); // At the current index, remove one element
  }
  if (subjects[i] == "History") {
    subjects.splice(i, 1);  // At the current index, remove one element
  }
}

console.log(subjects);

Answer 2

var index = array.indexOf('history');
if (index > -1) {
    array.splice(index, 1);
}

splice的第二个参数是要移除的元素个数。请注意，splice 会就地修改数组，returns 一个包含已删除元素的新数组。

Answer 3

使用splice:

var subjects = ["Maths", "History", "English", "Science", "Spanish", "Physical Education", "History", "English", "Science", "Maths", "History", "English", "Spanish", "Physical Education"];
    
function remove(arr, item) {
    for(var i = arr.length; i--;) {
        if(arr[i] === item) {
            arr.splice(i, 1);
        }
    }
}
    
remove(subjects, "Spanish");
remove(subjects, "History");

document.write(subjects);

输出：

[ 'Maths',
  'English',
  'Science',
  'Physical Education',
  'English',
  'Science',
  'Maths',
  'English',
  'Physical Education' ]

Answer 4

如您所知，删除运算符只是删除数组中某个位置的项目。这个位置仍然存在，但是 space 中的内容现在只是空的（数组可以有空的 space）。参见 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete#Deleting_array_elements

您可以使用拼接（参见 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice）按索引位置删除项目。

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];

for (var i = 0; i < subjects.length; i++) {
   if (subjects[i] === "Spanish") {
     subjects.splice(i, 1);
   }
   else if (subjects[i] === "History") {
     subjects.splice(i, 1);
   }
}

console.log(subjects);

或者您可以使用过滤器（参见 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter）：

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];

var isSubjectILike = function(subject){
    return subject !== "Spanish" && subject !== "History";
};
subjects = subjects.filter(isSubjectILike);

console.log(subjects);

Answer 5

你可以这样做：

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];
var index = subjects.indexOf("Spanish");
subjects = Object.assign(subjects.slice(0, index), subjects.slice(index + 1, subjects.length -1);

或者使用 ES6 过滤器：

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

var subjects = [
  "Maths", "History", "English", "Science", "Spanish", 
  "Physical Education", "History", "English", "Science", 
  "Maths", "History", "English", "Spanish", "Physical Education"
];
subjects = subjects.filter((value)=> value!="Spanish");

Answer 6

试一试：

for (var index in subjects){
    if (subjects[index] == "Spanish"){
        subjects.splice(index,1);

    }
    if (subjects[index] == "History"){
        subjects.splice(index,1);

    } 
}

如何从 JavaScript 数组中删除项目？

How do I remove items from a JavaScript Array?

javascript

arrays

delete-operator