Deep Copy of an Object in Javascript

function deepCopy(oldObj) {
    var newObj = oldObj;
    if (oldObj && typeof oldObj === 'object') {
        newObj = Object.prototype.toString.call(oldObj) === "[object Array]" ? [] : {};
        for (var i in oldObj) {
            newObj[i] = deepCopy(oldObj[i]);
        }
    }
    return newObj;
}