JavaScript JSON.stringify无法正确处理原型吗? [英] Javascript JSON.stringify doesn't handle prototype correctly?

问题描述

我一直在初始化这样的可重用类(构造函数通常是复制构造函数):

I've been initializing my reusable classes like this (constructor is usually a copy-constructor):

function Foo() {}
Foo.prototype.a = "1";
Foo.prototype.b = "2";
Foo.prototype.c = [];
var obj = new Foo();
obj.c.push("3");

，但是JSON.stringify无法产生预期的结果:

but the JSON.stringify does not produce the expected result:

JSON.stringify(obj);

{}

变量在其他所有方面均按预期工作.
如果toJSON被覆盖，则可以正常工作:

The variables work as expected for everything else.
If toJSON is overridden, it works fine:

Foo.prototype.toJSON = function () {
    return {
        a: this.a,
        b: this.b,
        c: this.c
    };
};
JSON.stringify(obj);

{"a":"1"，"b":"2"，"c":["3"]}

{"a":"1","b":"2","c":["3"]}

如果变量是在构造函数中定义的，它也可以正常工作:

It also works fine if the variables are defined inside the constructor:

function Alt() {
    this.a = 1;
    this.b = "2";
    this.c = [];
}
JSON.stringify(obj);

{"a":1，"b":"2"，"c":["3"]}

{"a":1,"b":"2","c":["3"]}

这是怎么回事?

此处的示例: http://jsfiddle.net/FdzB6/

推荐答案

通过引用对象，对象的原型(即其构造函数的原型)的属性可读:

Properties on an object's prototype (that is, the prototype of its constructor) are readable via a reference to an the object:

function Constructor() { }
Constructor.prototype.a = "hello world";

var x = new Constructor();
alert(x.a); // "hello world"

但是，这些属性确实卡在"原型对象上:

However, those properties really are "stuck" on the prototype object:

alert(x.hasOwnProperty("a")); // false

JSON序列化程序仅关注直接出现在正在处理的对象上的属性.这有点痛苦，但是如果您考虑反向过程，这有点道理:您当然不希望JSON.parse()将属性放回到原型上(无论如何还是很棘手的).

The JSON serializer only pays attention to properties that directly appear on objects being processed. That's kind-of painful, but it makes a little sense if you think about the reverse process: you certainly don't want JSON.parse() to put properties back onto a prototype (which would be pretty tricky anyway).

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