Is there something like object.toJSON in ES6?

Question

I'm using ES6 I transpile using Babel into ordinary JavaScript.

I want to serialise objects into JSON format and am wondering if ES5,ES6 offers a convenient function to do so.

For Maps and Sets there is a toJSON()-function proposed in ES7

Answer 1

You can use JSON.stringify and pass any kind of variable to it (given that it can be represented in JSON).

It works in all current browsers; in case you need a fallback for a really old browser, you can use Crockford's JSON-js.

However, keep in mind that, regarding objects, only public properties are serialized. There's no a generic way to serialize function variables etc. on the fly.

This is why some special object types provide a toJSON or similar method. In order to use such a function for arbitrary objects, you must pass a function as second parameter to JSON.stringify which checks for the existence of a toJSON function.

For example, the following should work (not tested, just from the top of my mind):

var jsonString = JSON.stringify(someLargeObject, function(key, value){
    return (value && typeof value.toJSON === 'function') 
        ? value.toJSON()
        : JSON.stringify(value);
});

If your someLargeObject contains a sub-object with a toJSON method, this code would use the object's implementation, otherwise use JSON.stringify.