Type / Constructor testing utilities

Question

My argument sanitization lib has a byproduct which does some typechecking and constructor investigation. I'm unsure if I'm using the fastest / most efficient approach here.

What are your opinions? Total rubbish or does it have a right to exist? ;)

// Return the type of an object aka safe typeof
function typeOf(o) {
    return Object.prototype.toString.call(o).match(/(\w+)\]/)[1];
}

// Return the name of a function aka class name
function nameOf(o) {
    return typeOf(o) == "Function"
        ? Function.prototype.toString.call(o).match(/function\s?(\w*)\(/)[1]
        : false;
}

// Return the expected arguments of a function
function argumentsOf(o) {
    if(typeOf(o) == "Function") {
        var args = Function.prototype.toString.call(o).match(/\((.+)\)\s*{/);
        if(!!args && !!args[1]) return args[1].replace(/\s+/g, "").split(",");
        else return [];
    } else return false;
}