为什么 JSON.stringify 不显示作为函数的 object 属性？

Question

Why doesn't JSON.stringify() display prop2?

var newObj = {
  prop1: true,
  prop2: function(){
    return "hello";
  },
  prop3: false
};

alert( JSON.stringify( newObj ) ); // prop2 appears to be missing

alert( newObj.prop2() ); // prop2 returns "hello"

for (var member in newObj) {
    alert( member + "=" + newObj[member] ); // shows prop1, prop2, prop3
}

JSFIDDLE: http://jsfiddle.net/egret230/efGgT/

Answer 1

Because JSON cannot store functions. According to the spec, a value must be one of:

_{(source: json.org )}

---

As a side note, this code will make the functions noticed by JSON.stringify :

Function.prototype.toJSON = function() { return "Unstorable function" }

Answer 2

Here is another way with using a .prototype. You can add an function to stringify

JSON.stringify(obj, function(k, v) {
  if (typeof v === 'function') {
    return v + '';
  }
  return v;
});

Answer 3

It's not supposed to stringify methods (or any functions) - especially since most methods of built in objects (and thus the prototypes of any user-defined objects) are native code.

If you really need it to print your methods out, you can override your object's .toString method, but when you call JSON.parse on the stringified output, it will treat the method as if it were just a string, and to be able to call it as a function you'd have to eval it - a practice that is typically not recommended.