function isFunction(a) {
    return typeof a == 'function';
}

function isNull(a) {
    return typeof a == 'object' && !a;
}

function isNumber(a) {
    return typeof a == 'number' && isFinite(a);
}

function isObject(a) {
    return (a && typeof a == 'object') || isFunction(a);
}

function isString(a) {
    return typeof a == 'string';
}

function isUndefined(a) {
    return typeof a == 'undefined';
}