Falsey values in JavaScript

Question

I had an interesting interview question today that stumped me a little. I was asked about falsey values. So undefined, NaN, null, 0, and an empty string all evaluate to fals

Answer 1

They're also useful for setting default values...

function foo(bar){
    alert(bar || "default");
}

I know a lot of people try to do

if (typeof(foo) === "undefined"){}

to get around falsiness, but that's got its own problems because

typeof(null) === "object"

for some reason