JavaScript: Deep Copy Circular JSON

intro:

I'm trying to write a deep copy method, but need to keep track of my visited nodes, so that I can link to the previously visitedNode instead of deep copying forever until stack overflow.

attempts:

var visitedNodes = {};
var obj = {}; obj.a = obj;   // circular; can't use JSON.stringify)
var obj2 = {};

visitedNodes[obj] = "should need key obj (not obj2) to access this string";

console.log(visitedNodes[obj2]);    // logs the string unfortunately

I don't have a unique way of storing the memory location -- it stores itself at [object Object] and I can't use JSON.stringify because it's a circular structure

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I tried using var visitedNodes = new Map(); but still no dice

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My current approach is to utilize the Array.prototype.indexOf function, but I don't know if it works with circular structures either, because I'm getting a stack overflow here too!!!

this.clone = function (item, visitedNodes) {
    visitedNodes = visitedNodes || [];
    if (typeof item === "object" && !Array.isArray(item)) {
        if (visitedNodes.indexOf(item) === -1) {
            var cloneObject = {};
            visitedNodes.push(cloneObject);
            for (var i in item) {
                if (item.hasOwnProperty(i)) {
                    cloneObject[i] = this.clone(item[i], visitedNodes);
                }
            }
            return cloneObject;
        } else {
            return visitedNodes[visitedNodes.indexOf(item)];
        }
    }
    else if (typeof item === "object" && Array.isArray(item)) {
        if (visitedNodes.indexOf(item) === -1) {
            var cloneArray = [];
            visitedNodes.push(cloneArray);
            for (var j = 0; j < item.length; j++) {
                cloneArray.push(this.clone(item[j], visitedNodes));
            }
            return cloneArray;
        } else {
            return visitedNodes[visitedNodes.indexOf(item)];
        }
    }

    return item; // not object, not array, therefore primitive
};

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the question:

Anyone have any ideas for getting a unique memory address so I can determine if I've been to the Object's reference before? I believe I could construct a unique hash based off Object.keys() and Object.prototype.constructor but that seems absurd and will give false positives if constructor is the same and the child keys are the same as the parent