Use the second parameter of stringify, the replacer function, to exclude already serialized objects:

var seen = [];



JSON.stringify(obj, function(key, val) {

   if (val != null && typeof val == object) {

        if (seen.indexOf(val) >= 0) {

            return;

        }

        seen.push(val);

    }

    return val;

});

http://jsfiddle.net/mH6cJ/38/

As correctly pointed out in other comments, this code removes every seen object, not only recursive ones.

For example, for:

a = {x:1};

obj = [a, a];

the result will be incorrect. If your structure is like this, you might want to use Crockford's decycle or this (simpler) function which just replaces recursive references with nulls:

function decycle(obj, stack = []) {

    if (!obj || typeof obj !== 'object')

        return obj;

    

    if (stack.includes(obj))

        return null;



    let s = stack.concat([obj]);



    return Array.isArray(obj)

        ? obj.map(x => decycle(x, s))

        : Object.fromEntries(

            Object.entries(obj)

                .map(([k, v]) => [k, decycle(v, s)]));

}



//



let a = {b: [1, 2, 3]}

a.b.push(a);



console.log(JSON.stringify(decycle(a)))