detectar tipos de objetos

detect_types.js

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 (typeof a == 'object' && a) || isFunction(a);
}