如何可靠地检查对象是EcmaScript 6地图/集？ [英] How to reliably check an object is an EcmaScript 6 Map/Set?

问题描述

我只想检查一个对象是 Map 或设置而不是 Array 。

I just want to check that an object is a Map or Set and not an Array.

检查数组我使用lodash的 _。isArray 。

to check an Array I'm using lodash's _.isArray.

function myFunc(arg) {
  if (_.isArray(arg)) {
    // doSomethingWithArray(arg)
  }

  if (isMap(arg)) {
    // doSomethingWithMap(arg)
  }

  if (isSet(arg)) {
    // doSomethingWithSet(arg)
  }
}

b $ b

如果我要实现 isMap / isSet ，它需要什么样子？我想让它能够捕获 Map / 的子类。如果可能的话，还要设置。

If I were to implement isMap/isSet, what does it need to look like? I'd like for it to be able to catch subclasses of Map/Set if possible as well.

推荐答案

情况与前ES5方法类似，可以正确可靠地检测数组。请参阅这篇精彩文章 isArray 的可能缺陷。

The situation is similar to pre-ES5 methods to detect arrays properly and reliably. See this great article for the possible pitfalls of implementing isArray.

我们可以使用

• obj.constructor == Map / 设置，但不起作用


• obj instanceof Map / 设置

• obj [Symbol.toStringTag] ==Map / 设置，但可以轻易被欺骗。



• obj.constructor == Map/Set, but that doesn't work on subclass instances (and can easily be deceived)
• obj instanceof Map/Set, but that still doesn't work across realms (and can be deceived by prototype mangling)
• obj[Symbol.toStringTag] == "Map"/"Set", but that can trivially be deceived again.

要真正确定，我们需要测试一个对象是否具有 [[MapData]] / [[SetData] ] 内部插槽。这不是那么容易访问 - 它的内部。我们可以使用hack，虽然：

To be really sure, we'd need to test whether an object has a [[MapData]]/[[SetData]] internal slot. Which is not so easily accessible - it's internal. We can use a hack, though:

function isMap(o) {
    try {
        Map.prototype.has.call(o); // throws if o is not an object or has no [[MapData]]
        return true;
    } catch(e) {
        return false;
    }
}
function isSet(o) {
    try {
        Set.prototype.has.call(o); // throws if o is not an object or has no [[SetData]]
        return true;
    } catch(e) {
        return false;
    }
}

$ c> instanceof - 它是简单，可理解，性能和工作在最合理的情况下。或者你立即去鸭子输入，只检查对象是否有 / get / set / delete / add / c $ c>方法。

For common use, I'd recommend instanceof - it's simple, understandable, performant, and works for most reasonable cases. Or you go for duck typing right away and only check whether the object has has/get/set/delete/add/delete methods.

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