test if two JSON objects are equivalent

JSON Object Equality.js

/**
 * not so simple check for object equality
 */
var equal = function(a, b) {
    function check(a, b) {
        for (var attr in a) {
            if (a.hasOwnProperty(attr) && b.hasOwnProperty(attr)) {
                if (a[attr] != b[attr]) {
                    switch (a[attr].constructor) {
                        case Object:
                            return equal(a[attr], b[attr]);
                        case Function:
                            if (a[attr].toString() != b[attr].toString()) {
                                return false;
                            }
                            break;
                        default:
                            return false;
                    }
                }
            } else {
                return false;
            }
        }
        return true;
    };
    return check(a, b) && check(b, a);
};