Javascript 获取数组中的最后一项
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Get the last item in an array
提问by balexander
Here is my JavaScript code so far:
到目前为止，这是我的 JavaScript 代码：
var linkElement = document.getElementById("BackButton");
var loc_array = document.location.href.split('/');
var newT = document.createTextNode(unescape(capWords(loc_array[loc_array.length-2])));
linkElement.appendChild(newT);
Currently it takes the second to last item in the array from the URL. However, I want to do a check for the last item in the array to be "index.html"and if so, grab the third to last item instead.
目前它从 URL 中获取数组中倒数第二个项目。但是，我想检查数组中的最后一项"index.html"，如果是，则改为获取倒数第三项。
回答by Aaron Harun
if (loc_array[loc_array.length - 1] === 'index.html') {
// do something
} else {
// something else
}
In the event that your server serves the same file for "index.html" and "inDEX.htML" you can also use: .toLowerCase().
如果您的服务器为“index.html”和“inDEX.htML”提供相同的文件，您还可以使用：.toLowerCase()。
Though, you might want to consider doing this server-side if possible: it will be cleaner and work for people without JS.
不过，如果可能，您可能想考虑在服务器端执行此操作：它会更干净，并且适用于没有 JS 的人。
回答by kritzikratzi
Not sure if there's a drawback, but this seems quite concise:
不确定是否有缺点，但这似乎很简洁：
arr.slice(-1)[0]
or
或者
arr.slice(-1).pop()
Both will return undefinedif the array is empty.
undefined如果数组为空，两者都将返回。
回答by mohawke
回答by Aram Kocharyan
A shorter version of what @chaiguy posted:
@chaiguy 发布内容的简短版本：
Array.prototype.last = function() {
return this[this.length - 1];
}
Reading the -1 index returns undefinedalready.
读取 -1 索引undefined已经返回。
EDIT:
编辑：
These days the preference seems to be using modules and to avoid touching the prototype or using a global namespace.
如今，偏好似乎是使用模块并避免接触原型或使用全局命名空间。
export function last(array) {
return array[array.length - 1];
}
回答by Josh Click
Two options are:
两个选项是：
var last = arr[arr.length - 1]
or
或者
var last = arr.slice(-1)[0]
The former is faster, but the latter looks nicer
前者更快，但后者看起来更好
回答by ucefkh
Here's how to get it with no effect on the original ARRAY
这是在不影响原始数组的情况下获得它的方法
a = [1,2,5,6,1,874,98,"abc"];
a.length; //returns 8 elements
If you use pop(), it will modify your array
如果您使用 pop()，它将修改您的数组
a.pop(); // will return "abc" AND REMOVES IT from the array
a.length; // returns 7
But you can use this so it has no effecton the original array:
但是您可以使用它，因此它对原始数组没有影响：
a.slice(-1).pop(); // will return "abc" won't do modify the array
// because slice creates a new array object
a.length; // returns 8; no modification and you've got you last element
回答by ddd
The "cleanest" ES6 way (IMO) would be:
“最干净”的 ES6 方式（IMO）是：
const foo = [1,2,3,4];
const bar = [...foo].pop();
This avoids mutating foo, as .pop()would had, if we didn't used the spread operator.
That said, I like aswell the foo.slice(-1)[0]solution.
如果我们不使用扩展运算符foo，这.pop()将避免 mutating 。
也就是说，我也喜欢这个foo.slice(-1)[0]解决方案。
回答by Pablo Mescher
I'd rather use array.pop()than indexes.
我宁愿使用而array.pop()不是索引。
while(loc_array.pop()!= "index.html"){
}
var newT = document.createTextNode(unescape(capWords(loc_array[loc_array.length])));
this way you always get the element previous to index.html (providing your array has isolated index.html as one item). Note:You'll lose the last elements from the array, though.
通过这种方式，您始终可以获取 index.html 之前的元素（前提是您的数组已将 index.html 作为一项隔离）。注意：不过，您将丢失数组中的最后一个元素。
回答by terribleWeb
I think if you only want get the element without remove, is more simple use this:
我认为如果你只想在不删除的情况下获取元素，使用这个更简单：
arr.slice(-1)[0]
Note: If the array is empty (eg. []) this will return undefined.
注意：如果数组为空（例如[]），这将返回undefined.
by the way... i didnt check performance, but i think is more simple and clean to write
顺便说一句......我没有检查性能，但我认为写起来更简单和干净
回答by Jamie Mason
const [lastItem] = array.slice(-1);
const [lastItem] = array.slice(-1);
Array.prototype.slicewith -1 can be used to create a new Array containing only the last item of the original Array, you can then use Destructuring Assignmentto create a variable using the first item of that new Array.
带有 -1 的Array.prototype.slice可用于创建仅包含原始 Array 的最后一项的新 Array，然后您可以使用Destructuring Assignment使用该新 Array 的第一项创建变量。
const lotteryNumbers = [12, 16, 4, 33, 41, 22];
const [lastNumber] = lotteryNumbers.slice(-1);
console.log(lotteryNumbers.slice(-1));
// => [22]
console.log(lastNumber);
// => 22