Lately, I've been delving into the realm of JavaScript WeakMaps. To my surprise, upon browsing through the documentation, I stumbled upon the fact that the clear method has officially been phased out with ECMAScript 6.
This raises the question: why have developers at ECMAScript chosen to eliminate this feature? What's the rationale behind mandating a custom clear function such as:
clear() {
this._weakmap = new WeakMap()
}
“The relationship between a weakmap and its key-value pair can only be manipulated by someone who possesses both the
WeakMapobject and the corresponding key. Without the ability to clear the mapping, individuals with access to just theWeakMapcould potentially impact the connection between the map and its values.”
The rationale behind this restriction stems from security concerns:
An important feature of Weak Maps is their non-enumerability of keys, which helps prevent malicious actors from observing the inner workings of other systems that share weakly-mapped objects. Allowing the collection's contents to be enumerated through the API could unintentionally create vulnerabilities.
tc39wiki
If WeakMaps were enumerable, it could also interfere with garbage collection by indirectly monitoring the process. Thus, the decision to exclude the clear method was made in the interest of maintaining a secure and predictable design.
The reason for its deprecation is that it hinders the implementation of an inverted WeakMap.
To learn more, visit Removal of WeakMap/WeakSet clear.
When WeakMaps/WeakSets cannot be inspected (via iteration) and lack a clear operation, utilizing the inverted implementation technique may be beneficial. This method reduces GS complexity significantly.
This concept of inverted implementation, as explained in the same source:
Creating an inverted implementation design:
Each object maintains a table internally (likely a hash table if it contains numerous elements) to carry out WeakMap/Set functionalities. Entries in this table consist of key/value pairs where the key represents a WeakMap/Set instance. Values are arbitrary ES values. This type of table is referred to as an "inverted map," with WeakMaps/Sets labeled as WCs.
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