Is there a way to test circular reference in JavaScript?

Question

I'm making a game, and I've come across a problem... When I try to save, JSON fails and reports that circular reference is being made somewhere. I don't think it actually is, I can't see it, so is there an algorithm or anything which could tell me where it is exactly (between which objects and stuff)? Also, is there a JSON alternative that can save circular reference? I'm running a node.js server, I saw this, but I can't get it to work (it's not made as a module i can require() in my code).

Answer 1

This is a small extension to Andris' answer that tells you where the first circular element is so you can deal with it accordingly.

function findCircularObject(node, parents, tree){
    parents = parents || [];
    tree = tree || [];

    if (!node || typeof node != "object")
        return false;

    var keys = Object.keys(node), i, value;

    parents.push(node); // add self to current path
    for (i = keys.length - 1; i >= 0; i--){
        value = node[keys[i]];
        if (value && typeof value == "object") {
            tree.push(keys[i]);
            if (parents.indexOf(value) >= 0)
                return true;
            // check child nodes
            if (arguments.callee(value, parents, tree))
                return tree.join('.');
            tree.pop();
        }
    }
    parents.pop();
    return false;
}

If you don't want a string, the tree array is unnecessary. Just change the original function to

return value;

for the circular object itself or

return parents.pop();

for its parent.