Gist showing how to JSON.stringify objects with circular references. Useful when dumping Express requests or dom.

stringify.json

// Note: cache should not be re-used by repeated calls to JSON.stringify.
var cache = [];
JSON.stringify(req, function(key, value) {
    if (typeof value === 'object' && value !== null) {
        if (cache.indexOf(value) !== -1) {
            // Circular reference found, discard key
            return;
        }
        // Store value in our collection
        cache.push(value);
    }
    return value;
});
cache = null; // Enable garbage collection