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';

}