Different output when using JSON.stringify

Question

I am using kendo UI, but i think this is a general question.

Basically I am logging a object the result looks like this,

Then I JSON.stringify(obj), i get the output like this

{"ProductID":5,"ProductName":"Cream","UnitPrice":12,"Discontinued":false,"UnitsInStock":15,"Priority":5}

Question , can someone illustrate why the parameters "dirty",'uid' does not get stringified ? It would be great if you could actually post some example creating such objects.

FYI: my actual object is like the output of stringify which is passed to a Kendo Grid and i get the dirty object from one of the kendo Grid methods (basically gives the set of rows thats been edited in the grid)

What is think its something to do with the object.prototype. Maybe the parent properties does not get stringified ...

Just something i noticed, the stringify seems to stop once it gets to thte _events and _handlers properties. which are objects, not like values that came before them. — Sean_A91
Can we see your code for where you create your object, and since we're at it, the line where you stringify it? — Sean_A91

T.J. Crowder T.J. Crowder · Accepted Answer · 2015-11-17T08:08:17

JSON.stringify only includes the object's own, enumerable properties whose names are strings. So there are three ways for properties to be left out: If they're inherited, if they're non-enumerable (such as those Object.defineProperty creates by default), or if their names aren't strings (ES2015 has the ability for properties to have Symbol names rather than string names).

This demonstrates two of those, the "own" and "enumerable" aspects: It logs {"answer":42}, for instance, because obj only has one own, enumerable property, answer. prop is inherited, and foo is non-enumerable:

// An object to use as a prototype
var proto = {
  prop: 1
};

// Create an object using that as its prototype
var obj = Object.create(proto);

// Define a non-enumerable property
Object.defineProperty(obj, "foo", {
  value: 27
});

// Define an own, enumerable property
obj.answer = 42;

// Show the JSON for the object
snippet.log(JSON.stringify(obj));

This is in the specification for JSON.stringify:

JSON.stringify calls the abstract specification operation SerializeJSONProperty
SerializeJSONProperty, for objects, ends up calling SerializeJSONObject
SerializeJSONObject calls EnumerableOwnProperties to get the list of properties to serialize

Live Example:

// An object to use as a prototype
var proto = {
    prop: 1
};

// Create an object using that as its prototype
var obj = Object.create(proto);

// Define a non-enumerable property
Object.defineProperty(obj, "foo", {
    value: 27
});

// Define an own, enumerable property
obj.answer = 42;

// Show the JSON for the object
snippet.log(JSON.stringify(obj));

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="//tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Just for completeness, this demonstrates Symbol-named properties being left out as well (live copy on Babel's REPL):

// An object to use as a prototype
var proto = {
  prop: 1
};

// Create an object using that as its prototype
var obj = Object.create(proto);

// Define a non-enumerable property
Object.defineProperty(obj, "foo", {
  value: 27
});

// Define an own, enumerable property with a string name
obj.answer = 42;

// Define an own, enumerable property with a Symbol name
var s1 = Symbol();
obj[s1] = "I'm enumerable and have a Symbol name";

// Show the JSON for the object
console.log(JSON.stringify(obj)); // {"answer":42}

// Proof that the Symbol property was enumerable comes
// from Object.assign
var obj2 = Object.assign(obj);
console.log(obj2[s1]); // I'm enumerable and have a Symbol name

Different output when using JSON.stringify

1 Answers