CODEWITHSUNDEEP
javascriptjsonfunctionobjectstringify
egret
egret

Reputation: 179

Why doesn't JSON.stringify display object properties that are functions?

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/

Upvotes: 11

Views: 7778

Answers (3)

Eric
Eric

Reputation: 97641

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

Valid JSON values
(source: json.org)

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

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

Upvotes: 24

Carol Skelly
Carol Skelly

Reputation: 362660

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;
});

Upvotes: 7

JKing
JKing

Reputation: 847

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.

Upvotes: 2

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