Javascript JSON.stringify function is not working

Question

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?

Answer 1

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.

Answer 2

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;
});

Answer 3

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"}"