Javascript 数据结构Javascript 数据结构

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#toc">在本文章中</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#.E5.8E.9F.E5.A7.8B.E5.80.BC">原始值</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#.E5.AD.97.E7.AC.A6.E4.B8.B2">字符串</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#.E5.AF.B9.E8.B1.A1">对象</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#Arrays">Arrays</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#Dates">Dates</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#WeakMaps.2C_Maps.2C_Sets">WeakMaps, Maps, Sets</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#TypedArrays">TypedArrays</a>

<a target="_blank" href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Data_structures#See_also">See also</a>

编程语言都具有内建的数据结构，但各种编程语言的数据结构常有不同之处。 本文尝试展现 JavaScript 语言中内建的数据结构及其属性，它们可以用来构建其他的数据结构， 同时尽可能的描述 JavaScript 数据结构与其他语言的不同之处。

ECMAScript 标准定义了 6 种数据类型:

Number

String

Boolean

Null

Undefined

Object

在下面的章节， 我们将看到这些数据类型如何被用于表现数据以及组合实现更复杂的数据结构。

在这些类型里面，只有4种类型被定义成常量<code>：true，false</code>，<code>null</code>，和<code>undefined</code>。 因为它们是常量，所以不能使用它们来呈现丰富的数据（或数据结构）。

依据 ECMAScript 标准，只有一种数字类型：它是一个基于IEEE 754标准的双精度64位二进制格式的值。所以它并没有为整数给出一种特定的类型。 除了能够表示浮点型的数值之外，还有一些带符号的值<code>：+Infinity，-Infinity</code>，和 <code>NaN</code> (非数值)。

尽管一个数字常常仅代表它本身的值，但JavaScript提供了一些位操作符。 这些位操作符和一个单一数字通过位操作可以用来表现一些布尔值。但这通常被认为是一个不好的做法，因为 JavaScript 提供了其他的手段来表示一组布尔值（如一个布尔值数组或一个布尔值分配给命名属性的对象）。 在一些非常受限的情况下，可能需要用到这些技术，比如试图应付本地存储的存储限制orin extreme cases when each bit over the network counts. This technique should only be considered when it is the last thing that can be done to optimize size.

不像 C 语言， JavaScript 字符串是不可更改的。这意味着字符串一旦被创建，就不能被修改。无论如何，它仍然可以通过新创建一个基于操作原字符串的新字符串（这么绕口），例如：通过String.substring, String.substr, String.slice, String.concat 等操作来修改原字符串时。

It can be tempting to use strings to represent complex data. They have a couple of nice properties:

It's easy to build complex strings with concatenation.

Strings are easy to debug (what you see printed is always what is in the string).

With conventions, it is possible to represent any data structure in a string. This does not make it a good idea. For instance, with a separator, one could emulate a list (while a JavaScript array would be more suitable). Unfortunately, when the separator is used in one of the "list" elements, then, the list is broken. An escape character can be chosen, etc. All of this requires conventions and becomes a maintenance burden which does not exist when the right tool for the right job is used.

It is recommended to use strings for textual data and symbolic data, but to parse strings and use the right abstraction for what it is supposed to represent otherwise.

Functions are regular objects with the additional capability of being callable.

Non-standard. Likely to be standardized as part of ECMAScript 6.

These data structures take object references as keys. A Set represents a set of objects, while WeakMaps and Maps associates a value to an object. The difference between Maps and WeakMaps is that in the former, object keys can be enumerated over. This allows garbage collection optimizations in the latter case.

One could implement Maps and Sets in pure ECMAScript 5. However, since objects cannot be compared (in the sense of "less than" for instance), look-up performance would necessarily be linear. Native implementations of them (including WeakMaps) can have look-up performance that is approximately logarithmic to constant time.

Usually, to bind data to a DOM node, one could set properties directly on the object or use data-* attributes. This has the downside that the data is available to any script running in the same context. Maps and WeakMaps make easy to privately bind data to an object.

<a target="_blank" href="https://github.com/nzakas/computer-science-in-javascript/">Nicholas Zakas collection of common data structure and common algorithms in JavaScript.</a>