function equal(a, b) {
        if (a === b) return true;
        if (a === undefined || b === undefined) return false;
        if (a === null || b === null) return false;
        // Check whether 'a' or 'b' is a string (primitive or object).
        // The concatenation of an empty string (+'') converts its argument to a string's primitive.
        if (a.constructor === String) return a+'' === b+''; // a+'' - in case 'a' is a String object
        if (b.constructor === String) return b+'' === a+''; // b+'' - in case 'b' is a String object
        return false;
    }
Compares equality of a and b
@param a
@param b