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本章将介绍由键索引的数据集合；Map 和 Set 对象包含可按插入顺序迭代的元素。

Objects and arrays can be painful to work with. Keyed collections such as Map, Set, WeakMap, and WeakSet make working with values or key-value pairs easier.

JavaScript has always allowed you to work with key/value pairs through objects. The Maps collection made available with ES6 improves on that. In this tutorial we cover Maps in full detail.

Map 对象保存键值对，并且能够记住键的原始插入顺序。任何值（对象或者原始值）都可以作为键或值。

Map is a collection of keyed data items, just like an Object. But the main difference is that Map allows keys of any type.

WeakMap 是一种键值对的集合，其中的键必须是对象或非全局注册的符号，且值可以是任意的 JavaScript 类型，并且不会创建对它的键的强引用。换句话说，一个对象作为 WeakMap 的键存在，不会阻止该对象被垃圾回收。一旦一个对象作为键被回收，那么在 WeakMap 中相应的值便成为了进行垃圾回收的候选对象，只要它们没有其他的引用存在。唯一可以作为 WeakMap 的键的原始类型是非全局注册的符号，因为非全局注册的符号是保证唯一的，并且不能被重新创建。

As we know from the chapter Garbage collection, JavaScript engine keeps a value in memory while it is “reachable” and can potentially be used.

Set 对象允许你存储任何类型（无论是原始值还是对象引用）的唯一值。

WeakSet 是可被垃圾回收的值的集合，包括对象和非全局注册的符号。WeakSet 中的值只能出现一次。它在 WeakSet 的集合中是唯一的。

As we know from the chapter Garbage collection, JavaScript engine keeps a value in memory while it is “reachable” and can potentially be used.

Google 会利用结构化数据标记来了解内容。请浏览本指南，了解结构化数据的工作原理、查看格式以及了解应将结构化数据放置在网站上的什么位置。

本章介绍按索引值排序的数据集合。包括数组和类数组结构，如 Array 对象和 TypedArray 对象。

Indexed collections in JavaScript - Arrays are the indexed collection in JavaScript as they allow us to access an element using its index.Following is the code to implement indexed collections in JavaScript −ExampleLive Demo

Lets dig into array methods like find, findIndex, includes, some, every and more to see how JavaScript helps us find out what is in our arrays.

JavaScript 类型化数组是一种类似数组的对象，并提供了一种用于在内存缓冲中访问原始二进制数据的机制。

Typed Arrays are an efficient way to store arrays of numbers that are of the same type - 8-bit integer, unsigned 16-bit integers, 32-bit floats, etc. This tutorial explains the basic idea behind them and provides a very basic code sample on how to create one and access it's values. The code gist includes links to the MDN documentation pages for all the main types and objects discussed. Code GIST: https://gist.github.com/prof3ssorSt3v3/8f879e711aee27d00cbc89d7c89f6668

But quite often we find that we need an ordered collection, where we have a 1st, a 2nd, a 3rd element and so on. For example, we need that to store a list of something: users, goods, HTML elements etc.

与其他编程语言中的数组一样，Array 对象支持在单个变量名下存储多个元素，并具有执行常见数组操作的成员。

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JavaScript 对象表示法（JSON）是用于将结构化数据表示为 JavaScript 对象的标准格式，通常用于在网站上表示和传输数据（例如从服务器向客户端发送一些数据，因此可以将其显示在网页上）。你会经常遇到它，所以在本文中，我们向你提供使用 JavaScript 处理 JSON 的所有工作，包括访问 JSON 对象中的数据项并编写自己的 JSON。

In this video we will cover everything you need to know about JSON in only 10 minutes. We will cover what JSON is, why JSON is important, what JSON is used for, the syntax of JSON, and multiple examples of JSON. JSON is the most popular data representation format, and is one of the most important, and easiest concepts you can learn in programming.