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<title>Document</title>
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<script>
let set = new WeakSet()
let key = {}
set.add(key)
console.log(set.has(key)) //true
key = { a: 1 } //移除了key的第一个引用，添加了新的引用
console.log(set.has(key)) //false， Weak Set中的引用也自动移除
</script>
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