如何在自定义toJSON方法中使用JSON.stringify？ [英] How do you use JSON.stringify in a custom toJSON method?

问题描述

因此，JSON.stringify提供了一个转换JS对象的好方法：

So, JSON.stringify provides a great way to turn a JS object like:

var baz = {"foo":1, "bar":someFunction};

输入JSON字符串，如：

in to a JSON string like:

{"foo":1}

它是这样做的一个可选的第二个参数，用于控制应序列化的字段：

It does this with an optional second argument that controls which fields should be serialized:

JSON.stringify(baz, ["foo"]);

这很好，但是有问题。假设您的baz实际上是另一个对象的属性，并且您想序列化该另一个对象：

That's great, but there's a problem. Let's say your "baz" is actually the property of another object, and you want to serialize that other object:

someObject.baz = {"foo":1, "bar":someFunction};
JSON.stringify(someObject, ["baz"]);

好吧，通常你只需要在baz上定义一个toJSON方法，例如：

Well, normally you would just define a toJSON method on baz, eg.:

someObject.baz = {"foo":1, "bar":someFunction};
someObject.baz.toJSON = function() { /* logic to "toJSON" baz*/ }
JSON.stringify(someObject, ["baz"]);

现在，正如我前面提到的，我们已经有了toJSONbaz的完美逻辑：

Now, as I mentioned earlier, we have the perfect logic to "toJSON" baz already:

someObject.baz.toJSON = function() {
    return JSON.stringify(baz, ["foo"]);
}

但是如果你试着把它放到你的toJSON中，你会得到一个递归错误，因为stringify将触发toJSON，这将触发stringify，这将...： - （

but if you try putting that in to your toJSON, you'll get a recursion error, because stringify will trigger the toJSON, which will trigger the stringify, which will ... :-(

你可以解决这个问题：

someObject.baz.toJSON = function() {
    var oldToJON = this.toJSON;
    this.toJSON = null;
    var ret = JSON.stringify(baz, ["foo"]);
    this.toJSON = oldToJON;
    return ret;
}

但是......这似乎是错误的。所以，我的问题是：你有什么办法可以利用漂亮的建筑 - 在JSON.stringify 里面一个对象的toJSON方法的序列化能力（在stringify操作期间不必隐藏toJSON方法本身）？

But ... that just seems wrong. So, my question is: is there any way you can utilize the nifty built-in serialization power of JSON.stringify inside a toJSON method of an object (without having to hide the toJSON method itself during the stringify operation)?

推荐答案

Crockford的json2.js 说：

toJSON方法没有序列化：它返回应该序列化的名称/值对所代表的值，如果没有任何序列化，则返回undefined。

A toJSON method does not serialize: it returns the value represented by the name/value pair that should be serialized, or undefined if nothing should be serialized.

因此，您只需返回要序列化的值。在您的情况下， baz.toJSON 应该只返回要序列化的 baz 对象的部分：

So you are simply expected to return the value that you want serialized. In your case, baz.toJSON should simply return the portion of the baz object that you want serialized:

someObject.baz.toJSON = function() {
  return { foo: this.foo };
};

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