有人可以帮助描述Javascript中的两种类型的数组存储吗？ [英] Could someone help describe the two types of array storage in Javascript?
问题描述
我正在 HTML5Rocks 上阅读有关V8的这篇文章。这篇文章很老了，但我几乎一无所知，这让我很烦恼。我一次采取这一步，但有人可以帮助我使用数组部分吗？
I'm reading this article about V8 on HTML5Rocks. The article is old but I understand almost none of it and it bothers me. I'm taking this 1 step at a time but could someone help me with the Arrays section?
文章指出：
数组
为了处理大型和稀疏数组，有两种类型的$ b内部$ b数组存储：
In order to handle large and sparse arrays, there are two types of array storage internally:
-
快速元素：紧凑型密钥集的线性存储
Fast Elements: linear storage for compact key sets
字典元素：哈希表存储，否则
最好不要让数组存储从一种类型翻转到
另一种类型。
It's best not to cause the array storage to flip from one type to another.
问题：
快速元素线性存储阵列会是什么样的？
What would a Fast Elements linear storage array look like?
词典元素哈希表数组会是什么样子？
What would a Dictionary Elements hash table array look like?
出于预防目的，我将如何从一种类型转换到另一种类型？
For prevention purposes, how would I "flip from one type to another"?
推荐答案
我会走另一条路。
2）字典元素
2) What would Dictionary Elements hash table Array look like?
JavaScript对象是从字符串到值的映射。例如
A JavaScript object is a map from string to values. e.g.
var obj = {
"name": "Sherlock Holmes",
"address": "221B Baker Street"
}
V8使用哈希表来表示对象，除非使用优化特殊情况的表示。这很像字典使用（单词，含义）对。
V8 uses hash tables to represent objects unless using an optimized representation for special cases. This is much like a dictionary uses (words, meaning) pair.
现在，这个哈希表访问速度很慢，因为最初哈希表中的所有键和值都是未定义。在插入新对时，计算散列并在插入索引处插入对。如果该索引处已有一个键，则尝试在下一个键处插入，依此类推。
Now, this hash table access is slow because initially all the keys and values in a hash table are undefined. On inserting a new pair, a hash is computed and the pair inserted at the insertion index. If there's already a key at that index, attempt to insert at next one and so on.
1）快速元素线性存储阵列是什么样的？
1) What would Fast Elements Linear storage Array look like?
在V8中，元素是属性，其键是是一个非负整数（0,1,2，...），即一个简单的线性数组，其属性可以通过数字索引访问。
In V8, an element is a property whose key is a non-negative integer (0, 1, 2, ...) i.e. a simple linear array whose properties can be accessed via a numerical index.
快速元素存储在连续的数组中。例如。
Fast elements are stored in a contiguous array. e.g.
var arr = [1, 2, 3];
它们是特殊情况，经过优化，可以更快地作为索引访问已知并且无法计算。
They are a special case that is optimised for faster access as the index is already known and not to be computed.
3）出于预防目的，我如何从一种类型翻转到另一种类型？
3) For prevention purposes, How would I flip from one type to another?
对于快速元素，如果指定的索引超出了元素数组的末尾，则V8可能会将元素降级为字典模式。
For fast element, if you assign an index that's way past the end of the elements array, V8 may downgrade the elements to dictionary mode.
参考： http ：//jayconrod.com/posts/52/a-tour-of-v8-object-representation
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