fix(map-and-set): Symbol as WeakMap Keys #1684
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現時点ではFirefoxは未対応だけど、文章だけの変更になるので入れてしまう |
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azu
commented
Aug 3, 2023
| @@ -307,7 +307,7 @@ obj = null; | |||
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| `WeakMap`は`Map`と似ていますがiterableではありません。 | |||
| そのため、キーを列挙する`keys`メソッドや、データの数を返す`size`プロパティなどは存在しません。 | |||
| また、キーを弱い参照で持つ特性上、キーとして使えるのは参照型のオブジェクトだけです。 | |||
| また、キーを弱い参照で持つ特性上、キーとして使えるのは参照型のオブジェクトと`Symbol`[^es2023]だけです。 | |||
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脚注にしているけど ES2023 でも別に問題ないかな。
SymbolがES2023のものに見えるのを回避したいぐらい
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概要
ES2022までは、WeakMapのキーとWeakSetの値にはオブジェクトのみが指定可能でした。
これは弱い参照をGCで解放するために、キーは一意な値のみが指定可能という制限からくるものでした。
Symbolも一意な値となるため、ES2023ではオブジェクトに加えてSymbolも指定できるように仕様が変更されました。
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