is.js

// by way of http://dmitry.baranovskiy.com/post/typeof-and-friends
function is(o, type) {
    type = String(type).toLowerCase();
    return  (type == "null" && o === null) ||
            (type == typeof o) ||
            (type == "object" && o === Object(o)) ||
            (type == "array" && Array.isArray && Array.isArray(o)) ||
            Object.prototype.toString.call(o).slice(8, -1).toLowerCase() == type;
}