WeakMap在EcmaScript5中的实现？ [英] WeakMap implementation in EcmaScript5?

问题描述

我已经跨越 JavaScript库实施跨浏览器 WeakMap 在 ES5 中。 （WeakMap将针对 ES6 计划。）

I've run across a JavaScript library that implement a cross-browser WeakMap in ES5. (WeakMap is slated for ES6.)

如果JavaScript语言本身没有支持，这可能如何工作？

How can this possibly work without support in the JavaScript language itself?

编辑：要清楚，我指的是一个弱地图，而不是一个常规的地图。我使用Chrome的分析器测试了这个项目，并且密钥没有强引用。他们得到GC，而不必将它们从WeakMap中删除。

Just to be clear, I'm referring to a Weak Map, not a regular Map. I tested this project out using Chrome's profiler and the keys are not held by strong references. They get GC'ed without having to remove them from the WeakMap.

推荐答案

我花了一段时间来挖掘代码，但是那么它打了我：键本身用于存储对该值的引用。

It took me a while to grok the code, but then it hit me: the key itself is used to store a reference to the value.

例如，几个层到 set 它是

defProp(obj, globalID, { value: store });

其中 defProp 已被定义为 Object.defineProperty ， obj 是关键， globalID 是一个guid和 store 是一个包含该值的存储对象。

where defProp has been defined to be Object.defineProperty, obj is the key, globalID is a guid and store is a storage object that contains the value.

然后在中获取它查找

obj [globalID];

这很聪明。 WeakMap实际上并不包含任何引用（weak或other） - 它只是设置一个秘密存储值的策略。使用 Object.defineProperty 意味着你不会意外发现价值存储 - 你必须知道查看它的魔术指南。

This is very clever. The WeakMap doesn't actually contain a reference to anything (weak or otherwise)-- it just sets up a policy of where to secretly store the value. The use of Object.defineProperty means that you won't accidentally discover the value storage-- you have to know the magic guid to look it up.

由于密钥直接引用该值（并且WeakMap不参考它），当所有对密钥的引用都消失时，它就像正常的GC一样。

Since the key directly refers to the value (and the WeakMap doesn't refer to it), when all references to the key are gone, it gets GCed like normal.

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