15

I have tried to convert a JS object into JSON.

JSON.stringify({a:1, toJSON: function(){}})

Native JSON stringify is not working as expected. JSON stringify executes toJSON function in JS object internally. I have overwritten native code as follows,

// Adding try catch for non JSON support browsers.
try{
 _jsonStringify = JSON.stringify;
 JSON.stringify = function(object){
    var fnCopy = object.toJSON; 
    object.toJSON = undefined;
    var result =  _jsonStringify(object);
    object.toJSON = fnCopy;
    return result;      
 };
}catch(e){}

It is working fine. is there any other better way to do this?. is there any specific reason in native code execute toJSON function in input object?

HILARUDEEN S ALLAUDEEN
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  • You should use [json2.js](https://github.com/douglascrockford/JSON-js/blob/master/json2.js) for browsers that do not support `JSON.stringify` – David Sherret May 27 '14 at 19:32
  • My questions are still pending ('is there any specific reason in native code execute toJSON function in input object?`). If anybody know reason, please update this thread. – HILARUDEEN S ALLAUDEEN May 27 '14 at 20:30
  • It's so you can customize the serialization. I've updated my answer with an example for you. – David Sherret May 27 '14 at 20:55

3 Answers3

13

This is because JSON.stringify will return the return value of the toJSON function if it exists (Source).

For example:

JSON.stringify({a:1, toJSON: function(){ return "a"; }});

Will return:

"a"

This behaviour is described on MDN. The reason for this is so that you can customize the behaviour of the serialization. For example, say I only want to serialize the IDs of the Animal class in this example. I could do the following:

var Animal = function(id, name) {
    this.AnimalID = id;
    this.Name     = name;
};

Animal.prototype.toJSON = function() {
    return this.AnimalID;
};

var animals = [];

animals.push(new Animal(1, "Giraffe"));
animals.push(new Animal(2, "Kangaroo"));

JSON.stringify(animals); // Outputs [1,2]

If you do not want this behaviour then your current method works well; however, I would recommend not overwriting the behaviour of JSON.stringify, but rather name your method something else. An external library might be using the toJSON function in an object and it could lead to unexpected results.

David Sherret
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0

The reason the native JSON.stringify doesn't work is because it can't stringify functions. By setting the only function, toJSON, to undefined, JSON.stringify returns the proper value. See this question for more details: JSON.stringify function

If you're trying to remove functions entirely, you can do this:

JSON.stringify(object, function(key, value) {
  if (typeof value === "function") {
    return undefined;
  }
  return value;
});
Community
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soktinpk
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  • Thanks dude, However my question is different. On executing `JSON.stringify({a:1, toJSON: function(){}})`, I am expecting `{"a":1}`. – HILARUDEEN S ALLAUDEEN May 27 '14 at 19:01
  • It is not working. I have tried `JSON.stringify({a:1, toJSON: function(){ return "Hello"; }}, function(key, value) { debugger; if (typeof value === "function") { return undefined; } return value; });` in chrome. Have you run this code? – HILARUDEEN S ALLAUDEEN May 28 '14 at 06:41
-2

The JSON.stringify function is usually invoked with one parameter, which is the object you want to serialize to JSON string. I believe there's a second optional parameter, which is a function that replaces one or more properties' way of serialization.

However, you should not add a function as a second property of your object!

When trying the following in Chrome's console:

JSON.stringify({a:1,b:'hello'})

This is the result:

"{"a":1,"b":"hello"}"
Jacob
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