Underscore.js deepClone function. Src is https://github.com/jashkenas/underscore/issues/162#issuecomment-2391752

deepClone.js

function deepClone (obj, depth) {
    var clone;

    if (!obj || (typeof obj !== 'object')) {
        clone = obj; // by value
    } else if (_.isString(obj)) {
        clone = String.prototype.slice.call(obj);
    } else if (_.isDate(obj)) {
        clone = new Date(obj.valueOf());
    } else if (_.isFunction(obj.clone)) {
        clone = obj.clone();
    } else if (_.isArray(obj)) {
        clone = Array.prototype.slice.call(obj);
    } else if (obj.constructor !== {}.constructor) {
        clone = obj; // by reference
    } else {
        clone = _.extend({}, obj);
    }

    if (!_.isUndefined(depth) && (depth > 0)) {
        _.each(clone, function (element, key) {
            clone[key] = deepClone(element, depth - 1);
        });
    }

    return clone;
};

Fixed to be validated in JSLint