javascript - 如何预先检查在将值添加到 JavaScript 中的 WeakSet 时不会抛出异常？

Question

考虑一个说明性的例子:

function addSafely(weakset, value) {
    if (canBeAddedToWeakSet(value)) {
        weakset.add(value);
    }
} 

那么，您认为在这种情况下实现canBeAddedToWeakSet 函数的简洁正确的方法是什么？性能也很不错。

我现在使用以下实现，但我不确定它是否完整(即涵盖所有情况):

function canBeAddedToWeakSet(value) {
    return !!value && (typeof value === 'object' || typeof value === 'function');
}

UPD:因此，这里有一些基准测试结果供那些对性能感到好奇的人使用。

• https://measurethat.net/Benchmarks/ShowResult/6648 (Chrome 61，Xubuntu 16.04)
• https://measurethat.net/Benchmarks/ShowResult/6649 (Firefox 52.3 ESR，Xubuntu 16.04)

Answer 1

引用ECMAScript 2015 (6th Edition, ECMA-262) WeakSet.add()

23.4.3.1 WeakSet.prototype.add ( value )

The following steps are taken:

1. Let S be the this value.

2. If Type(S) is not Object, throw a TypeError exception.

3. If S does not have a [[WeakSetData]] internal slot, throw a TypeError exception.

4. If Type(value) is not Object, throw a TypeError exception.

5. Let entries be the List that is the value of S’s [[WeakSetData]] internal slot.

6. Repeat for each e that is an element of entries,

   • If e is not empty and SameValue(e, value) is true, then
   • • Return S.

7. Append value as the last element of entries.

8. Return S.

正如项目 4 所说，它检查 type (ECMAScript Language Types) value 是否为Object，因为typeof null 也是'object'，所以函数canBeAddedToWeakSet 应该是:

function canBeAddedToWeakSet(value) {
    return value !== null && (typeof value === 'object' || typeof value === 'function');
}