在Javascript中查找数组长度 [英] Find Array length in Javascript

问题描述

这听起来很愚蠢。我们怎样才能在JavaScript中找到数组的确切长度;更确切地说，我想找到阵列中占据的总位置。

This will sound a very silly question. How can we find the exact length of array in JavaScript; more precisely i want to find the total positions occupied in the array.

我有一个简单的场景，我猜大多数人可能都知道。

I have a simple scenario which i guess most of you might be aware of.

var a = [1,2,3];
a.length; //This will output 3

现在，如果我给出

a[100] = 100;
a.length; // The output is 101; 

我想得到数组的确切大小，在上面的情况下应该是4。

I want to get the exact size of the array which in the above case should be 4.

推荐答案

这将为您提供数组中真正存在的元素数量：

This will give you the number of elements really present in your array:

Object.keys(a).length

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

编辑

正如JLRishe的评论所指出的， Object.keys（a）。length 返回对象a中存在的键数。
如果我添加这样的密钥：

As pointed in comments by JLRishe, Object.keys(a).length returns the number of keys present in the object a. If I add a key like that:

a= [1,2,3];
a['key']= "akey";

然后
Object.keys（a）.length 将返回4

但是key不是数组的一部分，它是数组Object的属性，
console.log（a） 给你[1,2,3]。

but "key" is not a part of the array, it's a property of the array Object, console.log(a) gives you [1,2,3].

因此，要获得数组中元素数量的更可靠值，我们只需要计算正整数键值：

So, to have a more reliable value of the number of elements in an array, we need to count only positive integer key values:

Object.keys(a).filter(function(el){return !(+el % 1) && +el>=0 && +el < Math.pow(2,32) ;}).length 

Object.keys返回一个String数组。使用 a ['1'] 或 a [1] 在数组中赋值是等效的。
数组索引键也必须小于2 ^ 32。

Object.keys returns an array of String. Assigning a value in an array with a['1'] or a[1] is equivalent. Array index keys have also to be less than 2^32.

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